Haha you've got some good choices! I guess I can give some short descriptions of these amps as I remember them.
My impressions of the GLMk2 was that it's a super punchy amp. I hadn't heard anything like it before and haven't heard anything like it since. I love the bass depth it has too, which is unlike any SS amp I've heard. Resolution is better than the RebelAmp, but not the last word, and soundstage can get congested and it can seem a bit compressed, which is ultimately why I sold mine.
The RebelAmp in comparison was literally a breath of fresh air. Soundstage was huge, the sound had awesome dynamic contrast, and everything felt more holographic and open. Bass, while not as punchy, was big and plentiful. Sub bass lost some of its impact, treble was a little rolled off, and it didn't seem as detailed compared to the GLMk2 (with and without the PSU). Timbre also seemed a bit artificially sweet, and voices could sometimes get hollow and not very realistic, sort of "holographic" in the "Princess Leia talking with R2D2" sense, lacking some heft and substance. Still very, very enjoyable though.
FA-10 for me is like having a good middle ground between the two, but with more resolution than either (as it should be for the extra cost and SIZE of the thing). Sounds are huge and immersive like on the RebelAmp, but the soundstage isn't quite as diffuse and the images get that solidity back. It has some very good punch and impact, but not at the same level as the GLMk2. The imaging is flawless, timbre is great, and it presents music in a very accurate way. Less aggressive than the GLMk2 and more weighty than the RA. I also have a BH Crack, so I wanted something with a less colored sound, and this definitely fits the bill. Despite that, the treble is very smooth and controlled, and it shares the Class A characteristic of things just sounding so big and lifelike. I'm using it with an HE1000 V2 right now, and I couldn't ask for more. Only downside is you can't use it as a preamp. Probably because it outputs 16 watts into 32 ohms...might be more realistic to power some passive speakers with it instead lol