I wouldn't say "better", both tetras can handle higher temps & are likely too big for betta snacks (as adults). I find both to be attractive I haven't kept giant bettas so I'm just guessing on that part.
I loved my kuhlis! I kept both striped & black. I prefer the striped for mellowness (less hyper) & prettiness. There are a few species of each; as always, try for all the same kind. My stripes (p. cuneovirgata) & blacks (p. oblonga) didn't interact at all except for a bit at feeding. No fighting but no mixing. I would say 8 is a good number for your tank.
I loved my kuhlis! I kept both striped & black. I prefer the striped for mellowness (less hyper) & prettiness. There are a few species of each; as always, try for all the same kind. My stripes (p. cuneovirgata) & blacks (p. oblonga) didn't interact at all except for a bit at feeding. No fighting but no mixing. I would say 8 is a good number for your tank.