I have used the one at Boggy Point at the end of Marina Rd, and it worked great, but you have to pick your times due to strong currents if you plan on sailing out under the bridge, especially in light wind conditions.

If you have Cat Tracks or similar beach wheels, the Gulf side you looked at might work just fine.

I wouldn't recommend the Cotton Bayou launch on the north side of the road due to extreme powerboat congestion and parking difficulties in the summer. Powerboaters don't like cat sailors, and unless you are a speed launcher, it just isn't worth the possible consequences. I have seen too many confrontations to make that seem like a good choice. It's hard enough to get in and out in a small powerboat on a weekend.