That is all going to depend on your build and your mod.
If you're building low (0.14 Ω), I recommend the LG HB6. If you're keeping your builds above 0.2 Ω, a Samsung 25R is fine. Above that, and you can rock an LG HG2.
If you have an 20700 compatible mod, the Sanyo 20700A is good, but hard to find. The Ampking/Ijoy/Golisi/Efest (all 5-leg tops) are good.
Learn your Ohms Law, and lookup Mooch here on ECF (he tests batteries).