As for name brand batteries, most ebay vendors advertize "high capacity" or "powerful", which is meaningless. I'd steer clear of vendors that state "samsung" without listing model number such as "Samsung INR18650-25R", which happens to have 2500mAh capacity per cell, and each cell has max discharge of 20A. For practical real world applications, you would never want to exceed 5A per cell max burst to preserve the life of your pack.
In short, you just don't know what you're getting if the vendor doesn't include a model number, and these companies all make batteries better suited for laptops and pocket calculators that would die an early death if used for high discharge applications.
Some cells have very high capacity (Ah) and some have very high discharge rates (A). Most are a compromise between the two. See the following table for capacity and discharge rating for commonly used brand name cells. Not all of these would be suitable for ebikes.
This is by no means a complete list, and misses many good cells for ebike applications. It is the best I could do on short notice.
Now for the Samsung 25R, I said the max you would want to draw is 5A per cell, but if you put 6 of these cells in parallel to make one large 15Ah 4.2V battery, your max amps would increase accordingly to 30A. In order to get a 48V battery, 13 of these parallel units would be put in series to increase the volts accordingly: 13 x 4.2V = 56.4V. Such a battery with 6 parallel groups (for 2500mAh x 6 = 15Ah) and 13 of these in series (4,2V x 13) would be denoted "13s6P, and such a battery would comprise of 78 18650 cells and weight about 4 kg.
My favorite model cells for batteries are MJ1, 35E, NCR18650PF, 30Q for high energy packs where you want a light pack but don't need something that can do 50A bursts.
For higher power, you usually have to compromise on capacity, and the Sony VTC3, VTC4, Samsung 25R would be better choices, and you wound build a higher capacity pack to allow higher safe amp draws.
I hope this helps clear up some of the mysteries surrounding cell choice. IMO, most of the ebay and amazon vendors are crooks selling misadvertised junk, and it is difficult to separate the wheat from the chaff. This is why we recommend dealing direct with vendors that actually construct the cells such as EM3EV.