I've done both. I've made new year's resolutions to stop cursing...HA! "not yet" and I've just gone into a new year without. I think NYR's are fine as long as you're resolving to do better.
While me cutting back on my profanity is a good idea, a better idea, is for me to pray more. While me saving more is a great idea, a better idea is for me to TITHE more. Is it clearer now? My suggestion is to not resolve to be better just for yourself, help someone out in the process. We've gotta move from self to others. If you're a follower of Christ, at some point you've gotta push yourself to do more for and in him. Love God, love yourself and love others. That's the best resolution you can give. Only what we do for God will last.