Yes after Labor Day is usually the best time to buy.
I would look at both new and used if I was you. Compare pricing. I would bet you can find a basically new boat for a great deal after the season is over.
As far as brands. That is going to depend a lot on what you are wanting to use the boat for. Deck boats are probably the most versatile boats on the water. You can fish, tube, ski, and cruise with plenty of space. Honestly I have never owned one but it is high on the list for my next boat.
V-bottom open bow run about will probably be one of the most available as well as pontoon. For brands it really depends on budget. Cobalt, Crownline, and Rinker are going to be towards the top but they are also the most pricey.
Probably the biggest piece of advice I can give you is stay away from anything that has carpet in it unless it is snap in carpet that you can easily remove. Most now a days are fiberglass floors.
As you start looking around if you have particular questions feel free to ask.