FBReader is also pretty good, and the free version allows plugins, which allows you to add the free TTS plugin. (Integrated TTS is in the paid version of FBReader.)

I also use Android's TalkBack mode with Kindle. It works well, since it auto turns pages for you. It needs to read whole pages at a time, so it's a bit of a pain re-reading things if you get interrupted. (Reduce the number of words per page to mitigate this.) It also puts a beep in each time the page turns (so don't reduce the words per page too low.) And it only keeps taking while you're screen is on, so it uses a lot more battery and will mess up your playback if the screen is touched. (Increase your screen on time in display settings so it reads for up to half an hour without touching the screen, or use Google Maps navigation overlay or some other method to force the screen to stay on indefinitely, if desired.)

I prefer a more monotone/robotic sounding voice for maximum consistency and to allow me to interpret tone, but there are lots of other TTS Engine options that can easily be added to Android if you prefer more natural sounding voices. That said, most have a much reduced maximum speed compared to Google's TTS option, so you might find other engines limiting once you get used to TTS if are looking to speed things up.

If anyone knows of a TTS with a faster maximum speed than Google's TTS, I would love to hear about it. I haven't found any faster ones in my searching, but there shouldn't be any technical reason why faster isn't possible.