RF, Orion, JBL, and Pioneer are all pretty good amplifier brands. I'd avoid the others.
As for 2-ch vs mono, that really has no bearing. What does matter, is the class of amplifier, and the quality of it's power supply. If this is to drive one or more subwoofers, you'll want a class D amplifier, as you can get them in larger output ratings, and they are much more efficient than class AB amps (which are 99.9% multichannel full-range amplifiers used more for cabin speakers, and not subs)
To keep things simple though, for asubs, stick to a monoblock class D subwoofer amplifier. Pick your sub(s) so it/they can be wired together to present a 2 ohm load into 1 channel. Then just get an amp that supplies somewhere in the ballpark of the combined RMS power handling ratings of the subs you chose. I'd suggest not exceeding that number, although having less than the RMS rated power of the subs is perfectly fine. You can't underpower a speaker. You can only overcompensate for lack of output by cranking the gains on the amp too high, causing the amp to clip, and frying the speakers' coils.
I'd only go with orion, jbl, or pioneer, as for the differences, it is just the quality of how they are built, jensen and kenwood get really hot and can overheat.
Orion, according to their reps at least, still use all milspec components to assemble their amplifiers, using high tolerance parts, and very ample power supplies. Good stuff.