Supposedly the Zippy "H" packs are the best, They had 3300mah 6s in stock a few weeks ago.
Make sure the cheaper bullets that the female end doesn't spin inside it's self, a little solder will cure it.
HC has great prices on heatshrink, Not the best of qaulity but plenty good enough.
The 6mm might still be out of stock in black ?
I retired from RC, now life is all about guns and long range shooting.