sony, samsung and perhaps lg... in that order.
the reason i place sony in the lead is that i believe they are still the only company which actually stocks replacement parts. samsung seems to be reputable as well. lg products are okay but their customer service is awful or so i've been told.
vizio, olevia, and pretty much any of the budget televisions are not worth your time. while they may be cheap and some people say they have had good luck with them if you do have a problem getting parts might be more involved than you would think. i have a relative who was a repair tech for 20 years.
if you want 3d you will want a 3d capable tv. if you want internet on the tv then you need the funtion. led backlit tvs will save quite a bit on your power bill over ccfl. if you plan to use the tv with a computer for gaming then you want a 60hz tv not 120 or 240 or you need to make sure the 60hz mode (game mode) actually works in the model you like.
for $600 you can get a 40" 60hz led sony bravia. you might have to look around for a sale or coupon but it is possible. it might be a barebones model (no 3d, no internet tv) but definitely a good choice.
i dont know if there is any best tv. ever person likes different models and brands depending on past experiences with the brands and personal perception (our eyes are all slightly different).