I have two quads with probably faulty VTX. Both BOSCAM. One with over-exposing image when under the sun. Indoors or with overcast it works all right. 

Second one despite being set to the right channel, seconds after connecting power to quad switches to random channel and spamming few others.

I am looking for a replacement for both. Still cheap. Not gonna buy ImmersionRC ones (no need for that) so.. what are the best options out there just now? I wasn't following VTX market in a while now.

i've been using those FX799s and they work wonders. The Foxeer Switcher vtx also works as well, but the last one I bought was faulty, not sure if there is qaulity control problem with the new batches though.
The problem with IRC ones is the size... simply too large for today's mini quad.

Over exposure would be a camera problem not vtx wouldn't it?

I've been using the new aomway raceband vtx with the boscam fr632 vrx, hs1177 camera and aomway clover+patch antennas on my quanum v2 for a while.
overall I'm very satisfied with the reception and video colors.
p.s
It's a bit tricky to tune the camera because the colors are more vivid through the vtx than directly from the camera to the screen