I haven't used a lawn vac personally, so take this with a grain of salt. But from what I've read here and elsewhere, the two main problems with lawn vacs in general are lack of power/suction, and dust coming through the bag.
The only lawn vac that I've seen that might be worth a look at is a new one from Bear Cat. Is has rotating bars in the front that pull up matted down lawn debris. And everything goes into a plastic can, maybe cutting down on the dust(?). I'm sure it's costly though.
What type of mower are you using, and do you have a bagger for it? This would be one way to go.
Good luck. And if you do get the vac, be sure to give us a review.