You're too educated to buy a steam toy. You're willing to pay to avoid temperature surfing and waiting to switch from frothing to brewing. You believe, as I do, that a two-boiler machine running effectively on only 110v sounds like an electrical engineer's fantasy. You love the romance of a piston machine, but cannot justify the inconsistent temperatures and resulting pulls. And you're not yet far enough along with your addiction (I mean "hobby") to need the divorce-inducing, 220v, direct plumbed commercial monstrosity. Sounds like you need a heat exhanger.
The Giotto's too expensive for no gain, the Oscar is plastic and missing a hot water wand, and the Expobar is just too primitive for you. Phew! I guess you just HAVE to choose either Tea or Livia. I suggest Tea and here's why (just pull up a chair):
Temperature stability – Tea’s E-61 has a ton of metal in it. As well, it circulates water through the group head back into the boiler, instead of being a simpler heat-sink (conductive heating) like Livia. Add to this Tea’s larger heater (1400 watt vs. 1200 watt) and a smaller boiler (1.4 Liter vs. 1.5 Liter). The physics suggest that Tea can regulate her boiler temperature and pressure within tighter tolerances with less effort: she would be quicker to recover temperature and less likely to overheat because she is recirculating temperature-regulated water, not relying on conduction from the overheated steam in the boiler. I can say that I have seen direct evidence of Tea’s pressure stability through my own observation. (I do not own a Fluke gauge, a la Schomer, so I cannot assert the related temperature stability directly.) With Livia I would always trigger the heater by venting steam and then pull my shot at her peak boiler pressure, watching the pressure gauge drop throughout the shot. With Tea I don’t even bother noting the boiler pressure because she can actually recover pressure while either frothing or pulling a shot.
Tea has an additional gauge for pump (or brew) pressure. I prefer using this as an additional indicator of shot quality: I can fidget with my grinder to pull a standard vs. ristretto shot and see the difference reflected in pump pressure as well as the resulting timed (by indication of proper extraction through lightening crema, not simple, chronological passage of time) volume.
Tea pre-infuses. It has been suggested that there are benefits from wetting the grounds before full pump pressure has built up to blast away at the top of your puck. I think a good tamp should probably take care of that, but if you have an off day and require a little help to keep those grounds in place, this is yet another point toward Tea’s forgiveness and resulting consistency.
I believe that there are fewer electronic parts in Tea, primarily around the portafilter backpressure release valve. My Livia’s flow meter ($37) died after 10 months of ownership (I bought her secondhand, mind you), disabling her auto-dosing features. When troubleshooting with a Whole Latte Love technician (that’s where she came from) I noted that Livia’s pressurestat releases a bit of wet steam right near the circuitboard as she reaches pressure. This odd design, along with comments from other sources about the general reliability of Livia’s electronics, did not reassure me. Tea’s mechanical pressure-release system not only looks and feels great, but it appears that there is less likely to go wrong than with Livia. (Yes, I know that Tea’s pump is activated by a button being pressed by the cam on the end of the lever, but the valve itself IS mechanical.)
By the way, everyone who has used both machines (I can personally vouch for a sample size of 6 people :) ) prefers using that cool lever mechanism over pushing a plastic-covered button. Come on! You’re an artiste, not an “operator.”
Tea is constructed from fully-polished, thick stainless steel. Livia looks great, but she has an exposed black frame and thinner metal all around. You might prefer that Livia is shorter, but in my book Tea easily wins this category. As well, the lighter weight and larger feet on Livia made her slide around my countertop significantly more than Tea, particularly when tightening and removing the portafilter.
Drip tray – Livia’s is smaller, plastic, and has to be tipped backwards to remove it. This is pretty nit-picky but there seems to be a large group in espresso-land that takes their drip trays VERY seriously. If you’re in this group, just forget you ever saw Livia. Along these same lines (picky even for me, and I’m a self-admitted caffeine nerd) is the whole reservoir debate. Livia has 118 ounces to Tea’s 98. I rarely filled Livia more than 2 inches above the low-water sensor because I just don’t want that much water sitting around getting stagnant near a heat source. Yes, Livia’s reservoir is bigger, but I have never run Tea out of water yet (I check her before each significant session). If you simply cannot be bothered to check water levels, then you should get Tea anyway, because you can retrofit her with either a direct-plumb or float-valve through Chris’ Coffee. If your entire decision hinges on a drip tray or reservoir, then you’re even more of a nerd than I, and it’s time for therapy. :)
Pod-capability – WLL indicates that Tea cannot use pods. If you spend a cool grand or more on an espresso machine and then allow ANYONE to use a pod near it, you should be ashamed of yourself. With that caveat, I guess Livia wins this point. ‘Nuff said.
Cup clearance under the portafilter spout – I insist on brewing directly into my pre-heated espresso or cappuccino cup. I am not about to lose all that crema and heat by transferring from a pitcher or shot glass to a second container (except at the very beginning when I was measuring everything to get the hang of it). All of my cups fit under Tea’s spout, but I have to tilt one of them ever so slightly. If you brew directly into larger mugs (again, shame on you, all that milk is just obfuscating your artfully pulled shot) then Livia wins by a hair in this category.
Livia is available in an auto-dosing version while Tea is not. Read up and you will understand that there are many variables in pulling a great shot. Volume is important, but more as an indicator of proper grind than a cause of a good pull. I prefer to end my shot when the crema lightens slightly, indicating the grounds are becoming overextracted. I do not mind if the volume or time are a little off of the “standard” (whichever one you choose). As such, once you spend a little time with your machine, I sincerely doubt you will continue to use the auto-dosing to “time” your shots. Livia’s auto features might help introduce a “disinterested co-user” like a houseguest or less-caffeinated significant other to the art of good espresso, but those features will inevitably hamper the true aficionado, and isn’t that for whom the machine is intended. Livia wins regarding this unnecessary feature (geez, can’t I give her even a little break?).
Wand access – I had Livia perched upon a dedicated 2-drawer base, which was handy. The few times I used her directly on the countertop, however, I was quite annoyed at the extra difficulty involved in placing and removing the frothing pitcher from a wand that could not change height. Tea’s vertical wand movement is, IMHO, a much better design allowing great access.
You get two dedicated portafilters with Tea and only one with Livia. I use Tea’s single spout portafilter for my backflushing disc so I don’t put extra wear on the spring securing the filter basket by switching it out every couple of days.
All this being said, Livia is a very strong performer. I would (and did), however, pay more for a Tea. I am most pleased with my decision.
(By the way, Don't even think of teaming Tea with anything short of a Mazzer Mini (Luigi). There IS no substitute.)