Adsense just yet. I think they still set the standards in PPC and they're a reputable company also. However, I'm waiting for YPN to get out of beta and go global. And I hope they'll do it soon 'cause a lot of us are missing the action.
I'm the same, I only use AdWords for PPC. However, there is a lot to become acquainted with AdWords, it really brings out the mathematical side of you when it comes down to conversion rates.
I'm only using Adsense and I'm not really making big bucks. I don't even reach $100 in a month. I know it's mainly my fault because I'm not doing enough advertising and SEO. But I'm actually thinking of trying another PPC. Maybe Adwords or TextAds.