What is your budget? If it's ~$140, the Herpstat ND is IMO the best. I have 10 or 12 of them. Not one has ever failed. If you have any questions, the owner of the company, Dion, has a very fast response time by e-mail, and is also a member here. The things I like about the Herpstat are- you set the temp- it accurately provides it. It has a high/low alarm. It's proportional, so it maintains a steadier temp than an on/off thermostat. You just set the temp, digitally, and that is what you get. No inaccurate dial. And i know Dion stands behind the product.
If you're looking for a cheap one, I would choose the Alife, which you can buy at The Bean Farm. I have a couple of these in use and they are simple and reliable.
I have in the past used the ZooMed 500R, and it's okay, a little tough to dial in, and I've had one or two fail. I've used the Big Apple current cheaper on/off model, and they were so whacky I took them out of use. Their _old_ model, which was almost identical to the Alife, was reliable.