never go for accounts that offer unlimited space or bandwidth as there is no such thing. make sure to check the company out, (best place to go is WHT forum and do a search for there company name and see if it turns up any info about them, if not make a post and ask if anyone has used them, addy is:
http://www.webhostingtalk.com ) read through the hosting company fourms and see how happy there customers are and if there are problems, and test there help support by pretending to be a current customer (if possible) that way you will find out what they are like. remember that YOU are resoponsable for your customers, ie if they upload illegal content or if they spam, your host may suspend your reseller account while they investigate. you should also know abit about webhosting before getting involved, remember its you who the customers will be asking questions to. on the up side though you dont have to worry about managing a server and making sure it runs smoothly and updating software etc, also most hosting companies will be helpfull and answer your questions. last bit of advice is that if you have the option of paying monthly or yearly you should choose monthly as if anything happeneds to the company thats your money and your customers money gone and you will end up with a lot of angry customers.
hope this helps you a bit