If you really want to surf - no leash - will teach you the appreciation of not bailing / taking the easy option - you will definitley surf better without the 'safety net' in small waves.
Otherwise, at a crowded break a 'comp' thickness leash should see you fine in small, weak waves. One important thing - check your leash for nicks / grazes - don't curl it around your fins and as soon as it has any breaks then replace it. If you're using it as a lifesafer the last thing you need is it breaking under straing when you most need it.
My personal preference is for creatures of leisure leashes - never let me down and last years - all the other makes I've had have all fallen by the wayside - I even had 2 FCS leases snap on me while paddling out