I first purchased a Snark SN-5. It looked great, tuned great but wouldn't auto-shut off, nor could I power it off with the single button on the front. It'd drain a battery in a day. I'm now using a Planet Waves two button version and it's working and lasting great.
I have a Snark and a Korg Pitchclip. The Snark is easier to use, but I think the Pitchclip is faster and more accurate. However, the Korg doesn't have the ability to recalibrate. Can't have everything, I guess.