Christina, it really depends on what you want to do with the internet. If you're mostly reading stuff and checking email then the basic package is good. If you want to watch episodes of the Sarah Connor Chronicles then the 3.0 package may be better, tho' the 1.5 would be suitable.
If you're not sure and want to spare the twenty bucks, get the 1.5. If you decide it's to slow call them and tell them you want to upgrade to the 3.0. It may take a couple of days for them to click the gui box but shouldn't be a problem for you.
CenturyTel doesn't describe their connection so I'll assume it a wireless modem in your home. If so, then you'll run the CAT5 from the wireless modem to your own router, then to your PC or wireless to your laptop. How you do that is none of their business. Don't give them extra money.
You might want to check out
BroadBand Reports to research. If in your area you can get
Clearwire, you might check them out as an alternative.