Which bike size should I choose?
I am looking for a bike online but just wondering I should choose 24" OR 26", my height is 5"6, 140 pounds.
Bikes are not generally sized by the wheel, except for possibly kid's bikes.
Are there any frame size measurements for the bikes you are looking at?
You really need to ride a bike before buying it. At Wal-Cr@p, bikes are sold by wheel/tire size (size 20, size 24, size 26, size 28) which has absolutely nothing to do with the size of the bikes.
If you were buying a traditional road bike at a shop, the staff would probably have you road test a bike in about a size 54 or size 55, and go from there. Most compact frame road bikes, mountain bikes, and hybrids use wierd sizing systems that can not be compared brand to brand.
The best bike is a bike purchased from a good bike shop. The best place to get fitted for a bike is at a good bike shop.