go for the lettuce one if you are going to go for it.
Most nudis are poisinous, either if eaten, or if they dies, they could harm your tank inhabitants (coral included)
Most nudis have very specific diets, and therefore starve in captivity.
The lettuce ones eat algae so thats easy!
They can also easily get sucked into powerheads and filters so you may have to make some modifications to these structures to keep him from getting hurt.
Heres my nudi, Ive had him for like 4 months or so.
they come in diff colors too, not just 'green' (the lettuce nudis) look here:
They do require extra care, but they are very cool IMO
Jessica/Shrimpi