The best router for you would eb the WRT54GL out of all the "G, S, L" models. Simply because it's alot more beefy that the normal WRT54G model, the Version 7 G model is very cut down in comparison.
The S model is speedbooster, which can be turned off leaving more memory for it to deal with other things.
The L model is basically a version 4 G model, which were THE best routers Linksys made in this series.
Ignore that it means linux as you'll notice no difference at all with regards to what actually runs on the router (you know, that drives the web-based interface and the hardware... etc?)
I have a "G" model (Version 5) and while it maintains itself okay now, it used to lock up alot due to it being cut down compared tpo the version 4's.
Oh my, i think i may have confused you with this post...
WRT54GL is the one for you
Also, you can set UPnP to on in the router which will take care of the ports for you.