I haven't tried Fantom packs yet, but most of my SMC packs last about 6 months in both my 1/10 4WD SC (2S) and 1/8 eBuggy and eTruggy classes (4S)

If your club allows it I would also consider ProMatch, they tend to last longer for me before they start to fade and generally have been my preference, with SMC as my backup option when ProMatch is out of stock for what I need, but if you're looking for a top performing pack, then I'd consider this one here before they go out of stock:
Product pages for Pro-Match Racing's rc lipo packs rechargable batteries

If you need an in-line, then this one here would be worth considering too:
Product pages for Pro-Match Racing's rc lipo packs rechargable batteries

I like to multiply the Capacity times the C rating to get the "Relative Amp" (rA) draw a pack can support, in the testing I've done, typically packs with the highest rA will offer the lowest IR.

I recently got this pack here for my 13.5T buggy and it was showing an IR of 1.53 which is pretty darn impressive for a 6Ah size shorty:
Product pages for Pro-Match Racing's rc lipo packs rechargable batteries