When I learned that Gunze Sangyo (Mr. Color) was going to be impossible to get in the states, I went out and stocked up. I'm sitting on (thankfully) about 200 bottles at the present time, and I'll cross the bridge of what to replace them with when the time comes.
I still have to use Tamiya for primary colors, black, white, etc. I have a drawer of MM, Polly-Scale, even some old Pactra, and for the most part, they sit there unless I desperately need a color that I don't have in Gunze.
Gunze, mixed with Dupont Centari Mid-Temp Reducer, is the absolute best paint I've ever used...period.
Once you've used it, you'll wonder how you managed without it.
As for Testors, I try to avoid using any of their products if I don't have to. I knew some of the original Floquil/Polly-Scale folks when I lived in NY, and I wasn't overly impressed with the way they were tossed aside when the big T bought them out.