America Online is the fastest growing and easiest to use in the opinion of many people. Prodigy has the best material for young children but has extensive financial services as well. One way to decide is to try them all since it's easy to sign up for a one month free trial and test each one. Of course if a service does not offer toll free access in your location, that could be a deciding factor. And even if you have a fast modem, a given service may not offer that speed in your area.
Help is available from many sources.
The providers have telephone help lines but the best way is to email your questions. Numerous books and periodicals are available in bookstores. CLMA is establishing a list of members who would be willing to answer questions as well. Of course you don't have to do it now and many people will wait. Waiting, however, puts you further behind and you lose the benefits of rapid information access and instant communication that are available today.