Well, first, I'd say don't count out the 20th Shiva because it doesn't use EL34s. I've heard, too, that the ones that do don't really have the magic that the KT88 version does. I'm usually an EL34 guy, too, but I don't miss them at all in my KT88 20th Shiva. It has all the cut and all the juicy mids. Honestly, if I didn't know that it wasn't EL34, I probably wouldn't know the difference. Anyway...
You mentioned the character of the JP2C vs the Mark V and I think that's a really good point. For me, I'd take character over versatility, but I also have more than a few amps. So, I think that part of your decision is deciding if you want something that has character or a jack of all trades. There are valid reasons for both...
Which leads me to ask, what kind of band are you wanting to start? If it's strictly a cover band that plays everything from George Jones to Slayer, a jack of all trades would likely be a good thing (if you're going for authenticity). If you're interested in finding your own sound (even if you're still only playing covers) or if you're wanting to play some or all original music, maybe a character amp would be better. Of course, that also adds the complication of whether or not the character of the amp fits your character and style. Mesas aren't Marshalls, Bogners aren't Friedmans, and Diezels are, well, Diezels. Some of them work for some players and some don't. That doesn't make one better or worse than the other, just different.
Another point to consider would be what your role in the band would be. Great rhythm amps aren't always great lead amps and vice versa. However, some are. If there's going to be another guitarist, you might want to consider what they'll be playing through and find something to compliment it. Something that sounds thin on its own often works much better in the context of a band, especially with multiple guitarists. On the other hand, being the only guitarist in a three-piece allows for a lot more room for the amp to fill.
You're likely right about regretting not having one after deciding on another... I think we're all afflicted with that disease here to a greater or lesser extent. You might want to consider looking at used options, too. That might allow you to sample multiple flavors within your current budget and it's usually easier to recoup more of your expenditure if you later decide to sell.
As far as reliability goes, within your list, I don't think you've got much to worry about. While it's true that some are better than others, they should all perform reliably unless you're overly abusive. Everyone builds a lemon every once in a while, but none of these companies got to where they are without having more great customer service days than terrible ones.
Anyway, I doubt any of this really makes your decision any easier, and this is all just my opinions, but I will say this. Try not to obsess too much and just pick one. Based on your list, you're not going to be terribly disappointed in any of them. I went through 7 or 8 amps until I found one that I was truly happy with (and I still have it), and I've probably been through at least 50 amps at this point. Some have stayed for awhile, some couldn't leave fast enough, but a lot of them are still around just because they all have one thing that they do better than everything else and they allow me to speak through them in a way I want to hear.
)
