Other than being inexpensive right now - those formats, especially the C - are very Albatros-like - they will both be extinct very soon. If you can, spend some money and join the digital age. You'll be glad you did.
Judging from past experience - the C "compact", gizmo, that allows you to insert and play the tape in any VHS machine - is prone to damage and then jamming in the machine.
The 8mm - not needing such a gizmo - of course does not have that problem. And it's real easy to hook-up your 8mm camcorder to your TV to view your tapes or copy them to VHS if you so desire.
I also like the way 8mm heads lay the signal down to tape better than the VHS method. I happen to think the 8mm tape cartridge itself is far superior than a VHS tape cartridge.
And in the end - the 8mm cartridge is still slightly smaller than the C cartridge. Smaller camera.