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.
Source
Also credit to Sempiternus for correcting my first answer
