My cicuit tester is a cheap, <$10, unit from Lowes. Happens to have a GFCI tester in it. As far as a multi meter, DMM, goes, I'd get 1 I can read the numbers on. Some are tiny and I can't see 'em. Otherwise cheap again is good. This is assuming a less than ideal environment. An analog meter is more helpful to me than a digital because when I'm doing continuity checks, I'd rather see the meter needle bounce than try to see the numbers count. Some, many, digitals have a buzzer for that purpose but I can't hear out of the left ear and I'm deaf in the right!!
Seriously, I have a VERY expensive DMM that I would cry if I ever dropped it in a puddle or if it crashed into the asphalt. Even though it has a rubber crash case. If I'm doing simple stuff like trailer lights and simple house hold stuff, the <$20 Radio Shack analog meter is just fine. Also, don't keep it in the general toobox where it can get smushed.