I've heard good things about Herpstats but I've personally only used Helix. I use them on my racks and incubator and have never had an issue.

Plus Helix has excellent customer service. I once blew a fuse on one of mine and Helix replaced it for free even though it was my fault.

I also hear that Helix has some really cool new features that are due to hit the market soon.

All that being said Helix has my vote