I bought a perfect fit deflector from http://www.carbras.com. I haven't seen an increadibly noticable reduction in the bug carcasses on my windshield. I pretty much wasn't expecting any miracles so I bought it pretty much for esthetics. Other folks might have seen different results from theirs though.
Maybe I installed mine wrong, but I installed a similar bug shield, as RedLava has, but mine blew off the front of my car while driving down that road. Luckily it landed in the field and I was able to retrieve it. Haven't tried to put it back on since that.
Make sure you loosen the four clamps so they are about ready to come off. Then push them against the hood as far up as they will go. They should sit in there firmly with the hood, you may have to wiggle them a little bit. Then tighten them down real good. The first few months I had mine I was constantly tightening the screws until I figured it out. Luckly mine never blew off.
I went with the VENTSHADE part# 2037. It does not and will not come in contact with the painrt. No rubber bumpers are needed to avoid paint contact and you can easily wash and wax the entire hood. I've had bug deflectors in the past that trap debris and make washing and waxing difficult.
I can't compare to the others as to the functionality, but I'd bet they are all about the same. The main feature is the ease of washing and waxing the hood.