I have learned a few things on the internet about the most important features in a modeler
1. Boot time
2. Boot time
3. Boot time
4. User Interface
5. Silver jubilee?
6. 5150?
7. Asshole in the room?
8. Does it chugg?
1,2,3: Boot time. When I used tube amps, I would make sure that I had my amp rig setup 30 minutes MINIMUM before the gig began to let the tubes warm up so my tone would be consistent. Then, especially in the winter, I had to wait 30 minutes for it to cool off before I felt comfortable putting it into the cold to drive it home.
4: User Interface (valid if you use the interface for editing). I would argue that this would be better divided into 2 categories: A) Ease of editing (either through a PC application, tablet, or front UI), and B) Ease of live playing operation (foot controller, live features, etc)
5,6: Replication of classic sounds. I would argue that this is valid for people that just want replication. Again, break this into 2 different categories: A) Replication of classic sounds. And B) Creation of desired sounds.
7: Amp in the room: Sadly, this is important to many people. Again, I would break it into 2 categories: A) Sounds good to guitar player and B) Sounds good in PA in the mix.
8: Does it chugg: Interestingly, I think this is more a matter of speakers than it is the digital or tube amp. If I have a high gain amp dialed in with a good amount of low frequency in it and run it through my full PA (double 18" subs and tops) .... OF COURSE it chugs. It will chug your heart into palpitations. Not sure this has much to do with the digital amp though.
This is at least a good start to a list of metrics that could be used to determine what a device is "best" at and how it compares to other units in the market.
I would defiantly add "durability" and "ease of stage setup" to this list as well as "expected longevity", customer support, and release to release stability of tone.
These are the kinds of things that I think should be evaluated in a review.