I have them all- Two Notes Live and Reload, Rockcrusher Recording, Suhr Reactive load, Aracom, Faustine, and some resistive ones (Komet Airbrake, Hotplate)... I have have used and tested them all extensively in my studio. I've also compared them all to loading with a real cab. In other words- I wasn't listening to the cab I was loading with, it was isolated in my live room, I was listening to the line out, into an IR in my computer, and then I'd disconnect the cab load and hook up each load box (or attenuator ) and could directly compare the sound of the loads that way to loading with the real cab (a /13 4-12" loaded with Greenbacks). I listened while playing and also recorded the results so I could listen back and really scrutinize.
I'm not going to rate them all against one another, but the most accurate sonically to loading to a real cab is the Suhr. It's basically indistinguishable from loading with a cab- the amp sounds/responds the same as with a 4-12" with greenbacks as the load. It's something you can measure as well and see on a scope. The others are really great as well, the closest sonically and measurement wise to a real cab as load is the Suhr. Yes I'm obviously a Suhr endorser but I also have great relationships with Rivera, Two Notes etc and I'm not here to blow smoke up anyone's ass- take it for what it's worth, I'm giving you the straight dope.
The Two Notes and Rock Crusher are very similar to loading with the real cab- with slight differences. I have used the TN units to great effect and I think they are terrific and great options, and the Rivera and TN Reload, with their switchable impedance, both get along great with my AC15 at 16 ohms (the AC15 only sounds good on the 16 ohm tap for some reason).... I plan on using them lots in the future and I also want to get the Fryette Power Station and give that a whirl.
The resistive loads all sound more midrangey and not as open. It's just the nature of the design... they don't have the high end rise and low resonant peak, that a cab has, or a reactive load designed to mimic a cab. Which isn't to say they suck, they just don't sound the same. You could hook up an EQ pedal and mimic some of what's changing using the resistive load, and I've done this and gotten good tones. My five minute lessons vol. 1/2 on my youtube were done this way (SL68-Hotplate-MXR EQ pedal_Matrilx power amp to reamp, into a 1-12" mic'd), I liked the tone lots.
Obviously the various units have various features and are at different price points, that will make them more or less attractive to different end users, for example the Two Notes Live also serves as an IR host, has digital out, is rack mountable, etc etc, it's a very well designed, elegant useful box. The Rivera also functions as an attenuator and has analog speaker simulation which may appeal to some dudes more than IR's... etc etc. The Suhr is the most inexpensive reactive box and is bare bones simple- it is really designed to be simple andsonically impeccable and for the recording guitarist mainly, although if you incorporate some other gear you can obviously load and reamp, etc.
So- it's not as easy as "which one's better?". It's "which one's better for YOU?"... at the price point you like, and with the feature set you need.
Incidentally, I wrote my Premier Guitar column on this subject this month, here's the link:
https://www.premierguitar.com/articles/2 ... and-reamps