Quite, fairly: khá + adjective

Khá before an adjective means "quite" or "fairly": more than a little, but less than rất. Phòng này khá rộng. This room is quite big. Anh nói tiếng Việt khá giỏi. You speak Vietnamese quite well.

It works with good and bad qualities alike: khá ngon (pretty good), khá xa (quite far), khá đông (fairly busy). In speech you'll often hear khá là: Quán này khá là ngon.

That's the difference from hơi (a bit). Hơi is usually for something a little too much or not quite right, like hơi mặn (a bit salty), so it rarely goes with praise. For praise, khá is the word: khá ngon, not hơi ngon.

Cũng before an adjective is cooler. Cũng ngon often means "it's OK, not bad", a polite, lukewarm verdict, though with a warm tone (cũng ngon đó!) it can be real praise. Khá ngon is a clearer compliment.

Tương đối (relatively) does a similar job, a little more measured in tone: Giá ở đây tương đối rẻ. Prices here are relatively cheap.