I bet this. Limpers are just that, limpers. They can come in with anything, small pair, Ax, Kx, suited connectors. Why would you be scared of J9? By betting you:

1. May get everyone to fold.
2. May get players holding a small pocket pair to fold.
3. You show aggression and will most likely have it checked around to you on the turn. If the turn misses you, you have the option to take a free card or if it hits you, bet again.
4. If the turn misses you and someone bets, there's a good chance you're beat so you fold.


By not betting I can almost guarentee that one of those three limpers will bet the turn and take down the pot. Most likely everyone will fold to him and you'll have no idea what he held.