Personally I like to use a variety of reality checks. Looking at your hand is nice and discreet, but I've found that it doesn't always make me lucid. However, usually it confuses me enough when I count six fingers multiple times that I just give up and do a nose RC, then become lucid. Overall I'd say the nose RC gives me the highest chance of becoming lucid, followed by the watch RC and then the hand RC, but it probably varies from person to person.

I don't think changing your RC will "reset" the work you have done. Most RCs work pretty much the same way. As long as you remember to do RCs (which you've already trained yourself to do, I'm assuming) during the day, you'll be more likely to do them while you're dreaming. It's remembering to ask yourself if you're dreaming when something weird happens that's important, not what you do to check whether or not you're dreaming.