Mesa Express 5:25
Mesa Express F-50
Mesa Express 5:50
I'll let someone with more experience with the other brands advise you on them, but for the Mesas, pass on the express series. It's an amp I was sure I was going to love based on the spec list, but then didn't really get on with. It's an updated F-series (the F-50 is just that, not Express F-50 but merely F-50), with additional gain modes, and adjustable "contour" mid shift instead of an on/off switch, and switchable poweramp wattage, from 5 wats to 25 or 50, depending on the model. Sounds absolutely awesome, and I was sure I was going to want to sell my Nomad after playing one.
However, after A/B'ing one with an F-30, I was let down. The clean didn't gush with quite the same lushness as the F-series in any mode or poweramp configuration, and the blues/burn gain modes were a letdown. Blues would have been a nice addition to the F-series, since it has a pretty fast ramp-up on the gain knob, but even I felt like burn was under-gained, and I take a lot of crap from my guitar buddies for being practically allergic to gain.
The switchable wattage was awesome, and the 'verb wasn't bad, but I couldn't get on with the actual tone of the amp itself. It was nice for lower gain blues/rock stuff, but if that's your thing any of the Lone Stars absolutely own it, anyway.
The F-series I'd still strongly recommend, especially since these days if it isn't used (and therefore cheap) it's being cleared out (and therefore cheap). Also, the DC series is worth a look too, as these were pretty much the precursors to the F's and are a little more Mark-like, which if you're into 80's tones may be even more your thing. I like the Nomads too - I ended up impulse buying a Rectoverb that day I was demoing the Express amps, and was so blown away once I got to really open it up that I haven't played my Nomad combo since really, but I can't quite briing myself to sell it.
The Express though... I know a few guys here like them, but I'm not one of them.