Paralysis is better
Mathematically, Sleep is better because it gives you a 2x multiplier, while Paralysis only gives you a 1.5x multiplier. However.......
You're better off paralyzing it, since although it has less of a catch rate than putting Pokémon to sleep, the Pokemon isn't able to recover from Paralysis (unless it has a statues healing move). However, the opposing Pokémon could wake up from sleep any turn, so it's not as good as paralysis.
Also credit to Sempiternus for correcting my first answer