On many digital-modeling amps, headphone-outputs are a definite plus! (Use some decent real, full-sized, closed-back headphones with 'em.)
Look for headphone-outs and speaker-compensated direct-outputs for connecting to recording devices and PA mains and monitors. Being able to go direct and play at relatively low volumes (and low stage-volumes) while still largely getting a sound like a miked, cranked-up tube-amp is a very useful thing!
Try various modeling-amps and/or other digital-modeling devices with your own guitars, and even your own pedals; putting a few of your favorite analog pedals in front of a modeler, especially one that 'takes pedals well', can further enhance the realism of the modeled amp sound and feel.
I was quite impressed with the sound of a Line 6 2x12 combo-amp a few years ago, that a guy playing in a band in my friend's tavern was using. I can't remember which specific model it was (all SS, not a Spider Valve, though perhaps a Spider or Vetta or... ?), and I didn't play through it myself; but I was surprised to find that it was a SS modeler that had caught my ear and impressed me from the other room.
A good friend who's an excellent player with a sharp ear loves and raves about the Line 6 Spider Valve and Spider Valve II line, which use a tube/transformer output-stage; I think I would like them, except that they need to be cranked and they're LOUD with a capital LOUD, and I've been heading the opposite direction- when in its "sweet-spot" zone, my 7 watt tube-amp head is actually too loud most of the time!
Speaking of which, I often go direct to PA mains and monitors with a digital-modeling/multi-effects unit, while also going to my low-watt tube-amp in parallel
with the modeler- that is, the next to last pedal in my chain has stereo outs, Left going to said tube-amp, Right going to the digital-modeler. This gives me a fatter, fuller, warmer tone than the modeler by itself, and a lot more additional flexibility and variety than the tube-amp by itself. It's sort of a poor-man's multi-amp rig.
put the modeler through any tube-amp, neither the input nor an effects-loop, as the modeler neuters the tube-amp and the tube-amp compromises the modeler. Though I have often gone direct with the modeler, without the tube-amp...
Yamaha's DG100- the 2x12 combo with the programmable motorized knobs and a number of effects- was excellent; you would do VERY well with a used Yamaha DG-series modeling-amp, particularly one of the models with the motorized knobs... Here's a good info-'page on the Yamaha DG-amps line