The shop that did my brake flush use Dot4 instead of the Dot3 I requested. It's been several years but I just realized that when I was checking the paperwork.

Since I need to flush the brake fluid due to the age and color, should I go back to Dot3 or keep the Dot4? What brand of fluid should I buy for the flush?

DOT 3 absorbs less moisture from the air, DOT 4 has a higher boiling point but absorbs more water thus requires more frequent changes. Don't use DOT 5.1 for street use, it has great track capability due to superior boiling point but it absorbs water RAPIDLY, sort of a track-use-only fluid.

Personally I use Valvoline DOT 3/4, it's synthetic has great pedal feel for street / light track use, and still has a pretty good lifespan, I replace it every 3 or so years and with my brake fluid hygrometer it only picks up about 3% moisture in that time, that's the thing about brake fluid interval, it's not exactly a set value it depends on your atmospheric conditions. You always want to replace it when replacing your brake pads but it can vary wildly how often you would change it for regular maintenance. That's why I usually just stick the fluid tester in the reservoir and replace it when it's at 3%.

Thanks for the info! What tester you use?

I like this one because there are dip switches on the back (on the back of the circuit board, requires disassembly to access) to calibrate it.