As @vwdstriker said, it all realy depends on what you are after… I wrote an article a while back on how to get the best battery for your drone. but this was aimed more at larger quadcopters where you want to fly as long as possible… but for FPV quads, you basicaly want a battery that can output the sufficient current for all your motors…
For example since you are using 4x 30A ESC… your motors will probably draw close to that on full power with 6 inch props… so you need a battery that can handle 120A of current…
99% of 5-6 inch prop FPV quadcopters will use 1300-1800mah lipos so you can get one of this size which is like the one @SmithQ suggested.
The only other thing you need to care about is that the 1300 has a sufficient C rating… so if you need to pull a max of 120A… then you need to make sure the C rating is at least 90C (90*1.3) = 117A which is close enough.
However since you will not be flying at full throttle all the time, you can probably get away with 75C… but dont get anything less than that.