I have found that it is better to buy cheap clothes that the kids like, because they will outgrow it or stain it before they wear it out.
I've had good luck with Carter's and Gerber. Carter's resists stains pretty well and seems to be very durable. Gerber is more of just onesies and pj's but I've liked them a lot too. They are a little more expensive, but I also have had good luck with Jellybeans and Old Navy.