you have to be a us resident though i believe for yahoo. but they have a higher average epc although the ads are not as targeted.
I believe it also depends on your niche like for "make money online" bidvertiser pays better than adsense. But to name some alternatives, you can try YPN, kontera, bidvertiser, chitika etc etc
Adsense is probably the best one. You'll make a lot with them. Adbrite i heard is good too but i don't like there text ads and full page ads. Adbrite takes 2 months to pay. I don't like that either
I currently use seven different ppc/pps sites and Etology has worked the best for me so far. I've made four times more money with them than my second highest ppc which is adbright (a.k.a. avnads).
I too have to vote for AdSense on this front. To date I have struggled to find any to me similarly profitable PPC program.
Adsense and YPN are very good for a lot of niches If you have an entertainment type of niche then they may not be as good for you as some other niches would be when using these programs.
Well an alternative could be Bidvertiser they pay by paypal you can be in any country and I know some friends that make some pretty good money with them