We use a lot of CFLs and the old big round ones with a center adaptor.
The real cheapies seem to have short life ballasts.
Lights Of America (made in China) has a HECK of selection, and we haven't had one go out yet (5 years-ish? Using a dozen bulbs daily) Their efficiency is better than most, and thats what you are looking for, right? Plus, they are reasonable.
I got the first ones at an end of season clearance sale (End of light bulb season???), only because the price was 90% off. I'm a cheap SOB.
You can get them at your local Wally-Mart. Remember to check the Clearance Section! I got a slew of assorted fluorescent bulbs (just the bulbs) for 5 cents each a while ago. I can't wait to use one.
The chain home improvement center should all have them.
Sam's Club here just had a 6 Pack of LoA brand 13 watt CFLs for $9
GE makes some good ones too, but I think a lot of them are still a Lights of America light in a different package.
IKEA had a bunch of skids of CFLs the only time I was ever in one, 2 years ago. I only used 1 so far, as I'm stocked from all the clearace sales, but in my kids bedroom for 2 years now. They were almost free! I recall the 7 watt was $1.50. Their selection went to 20-something watts for $4 (?).
My choice would be Lights of America, even if they cost more.
I've changed the bulbs, but suspect the ballast usually ruined them, because the replacement bulbs at best last a few weeks. I go 1 piece now and change the whole thing, now the cost is so low. (I already said I am a cheap SOB, remember?)
Hope I helped