One thing to be certain of with any router is to be sure its encryption protocol can be set to WPA2/AES. I'm not sure the older ones can be set to that. They may use WEP, which can be cracked in under a minute or WPA, which has also been broken. You also want to set a very long, all over the keyboard router password. Just keep it safe somewhere and don't lose it. Mine is 40+ characters and no one's going to guess it.
You are basically broacasting all your data, i.e. passwords, sensitive or personal information, and you want to be sure it can't be read.
And, whatever router you settle on, do not set up the router security with any automatic feature. You want to avoid those and do it all manually. These have been easily cracked.
And the stock Linksys firmware for the WRT54GL, though not bad, can easily be replaced with a superior one, "Tomato." If you're not up to doing that, there's no problem keeping the original Linksys firmware.
http://www.polarcloud.com/tomato
http://lifehacker.com/344765/turn-your-60-router-into-a-user+friendly-super+rout er-with-tomato