Hehe, I gotta agree with Ryandor here. I voted for Sphere because well, it'd be treason if I didn't (being a sphere dev I should be at least a LITTLE loyal *grin*) but I also think that no one can say there is a 'best' emu. They've all got faults and bonuses.
Sphere I like best because I don't need a phd in computer science to use it. The scripting syntax (up until recently at least *grumble*) was pretty simple to catch on to in a matter of minutes/hours. It's very powerful if you know what you're doing with it, newer releases are even more so, but lost a good chunk of the user-friendliness. I love the fact there's a HUGE community, and help can be found 24 hours a day on just about anything. I love the fact that every program I could ever need is available for it and fairly easy to find. I hate the fact that bug fixes are at the mercy of just a couple devs, they have lives and can't work on it as fast as I'd love to. I hate the fact I can't program and help them with it :p I hate the fact that with a community the size of Sphere's, new bugs become a plague within minutes of being found, game-breaking exploits included, and aren't fixed nearly as fast.
UOX variants I like because they're familiar enough to be comfortable (Sphere grew up side-by-side with UOX, so they're actually fairly similar). Lonewolf/Wolfpack have proven themselves to be reliable, but the rate of progress on them and scripting options I didn't care for. Nox Wizard has an excellent community. I was very impressed with the dev responses on their forums. Wasn't real fond of the Small scripting though (of course, I don't know it). Revelation I haven't tried, the community never kicked it off big enough to check out for me, and several of the posts made it look like they'd re-merge into Nox so it didn't strike me as being a stable project.
UOX3 (0.9x versions that is) I like because the JS engine is very powerful and not so hard that I can't understand how to use it, even though it takes me awhile to script something that works lol. The JS engine is more powerful than Sphere's scripting language in many ways, but more limited in others. The devs are wonderful, I tried out the latest test build of 97.0.something or other for a few days, every bug I found in it & reported was fixed within a day or two, re-compiled, and re-released. I'm normally not big on small communities, but I think UOX3's current community is wonderful. They're all very eager to help each other and get things fixed ASAP. Drawbacks would be the few crashing bugs remaining in it, but they're working them out. It's just not stable enough, RIGHT NOW, for a live shard. Some of the scripting in it I can't stand, and some of the things not allowed in it strike me as basic needed features for any emu. Another drawback would be the lack of 3rd party tools that work with their new save formats. Having the .wsc files all broken up into regions makes all the tools useless.
POL is amazing, when done right. Unfortunately it takes a rocket scientist to do it right. The scripting allows you to completely redo pretty much everything in the game, if you know how. Hardcoded bugs in the core can be scripted over, so waiting on devs to fix bugs isn't needed. This turns away most new users though unfortunately, as fixing critical bugs in the server isn't a new admins main desire when learning a completely new system. My main gripe about POL would be the in-game feel. Remember me saying UOX felt 'comfy' like Sphere does? Well, POL feels alien. The only words to describe it (and I stole this description from someone else that feels the same way lol) is that POL feels like an emulator of an emulator.. or fake somehow. Not trying to be a diss against POL lol, it's just weird feeling in-game. Another gripe would be the tech support, or lack thereof. I went on POL's irc server with a problem. There were 3 people there that knew what they were doing. I politely said hello and asked my question in a mature/detailed manner (explaining what the problem was and what I'd already tried to do to fix it). The first person completely ignored me, he continued talking to someone else in there about girlfriends and such. The second person typed *shrugs* and went afk. The third person was afk when I asked, but came back shortly thereafter, answered in a quick "hurry up and get your answer and go away already" manner, and went afk again. I mean.. jeesh, that's not a very convincing way to get or keep users. The answer, btw, was in some foreign language called eScripting that no newbie should hope to comprehend *grin*.
I've only ran RunUO for a matter of a few minutes on the first or second beta release, so nothing was working then. It felt 'ok' in game. The politics involved with RunUO are a turnoff for me though. I will never use it, no matter how amazing it ends up, simply because of that. I can't say much of what I *do* like about RunUO considering I've not used it enough to know shit about it, I do like the idea of having an entire programming language at your disposal to script, I do not like the idea of having to learn a programming language just to script something simple. I like the fact that they're releasing beta after beta very quickly and are showing tons of progress in a short time, I do not like the fact that they WILL burn out at that rate and closed source projects with burned out devs (like Sphere was for over a year) are very bad things. I do not like other things, but again.. those are mainly flames and personal opinions
Epsilon started out amazing. The scripting language looked insanely promising, and so close to Sphere (as in, easy to use AND similar enough that I already understood it) that I was drooling all over the place. In game it felt comfy. It started out quick and progress was excellent, then it just.. fizzled. Kair burned out I guess, then tried a C# version of it instead of VB then stopped altogether. Seems he's working on it again though, so hopefully it'll shape up into an excellent emu over the next few months.