Gunshows are *occasionally* a good place to buy, but MOST of the tables will be full of over-priced guns.  You also have some danger of dealers switching out parts and such, so you REALLY need to know EXACTLY what you're getting (and you cannot depend AT ALL on the dealer for this; many will lie to you).

In most cases, you're better off buying from a good local gunstore that you trust, and who will be in your area if something goes wrong.  You don't want to buy from a dealer, make a mistake, and have to drive hundreds of miles to get it fixed.

You DO know about the features restrictions currently on AR15s due to the Semiautomatic Assault Weapons Ban, and the fact that the Ban will be going away in a year, right?  A new rifle you buy today cannot have a collapsable stock, flash suppressor, bayonet lug, or grenade launcher.  In a year, most rifles will come with the first three.  You could also buy now and reconfigure later, but you'll spend money to do so.

I recommend reading the forums in the AR15 section that interest you, especially the posts tacked to the top of each forum, and otherwise read everything you can for a month or so.  If you have questions, ask (but try to find related posts first; we've probably answered it for someone else recently).  Especially, read the Optics forum, even if you don't plan on getting optics *now*.  Look through all the catalogs and websites, including the parts pages, not just the complete rifle pages.

Then, AFTER reading all of that, figure out what configuration you want.  Post that configuration and ask for opinions.  Don't be surprised if we suggest dropping some of the more "gimmicky" parts.    After all that feedback, go down to your local gunshop and order your rifle (or just the lower, allowing you to custom-order the upper and get it direct from the manufacturer).

Yes, this is more work up-front, but it will save you a lot of time, money, and aggrivation later reconfiguring your rifle because it isn't what you really wanted.

-Troy

The "Assault Weapons" Ban will necessarily expire; the sunset or expitation date is written into the bill itself.
There's no sure way to tell right now whether or not the current law will be replaced with something.
A new bill could be less stringent, similar to the existing one, or even stricter than current law.

I don't think you're being advised to wait on account of the "Assault Weapons" Ban issue, but rather to give you time to ponder the configuration of your AR