A little info on preapproval sites:
Discover: you can put in whatever you want and get a recommendation. You really are preapproved if the APR is a hard APR, so be sure to check that and don't just take the recommendation as gospel.
AMEX: pretty good on giving you some card options that you can realistically be approved for.
Citi: a little misleading because they will give you a bunch of cards they recommend so be sure to read the page.
Chase: probably the best preapproval page - if it's there it's highly likely that you'll be approved for the offer.
US Bank: it seems to have gotten a little more misleading recently, so be sure to see if you're offered a firm APR.
BOA: on par with Discover these days - you can put in whatever you want and get a recommendation - I put in Sponge Bob Square Pants living at 123 Pineapple Way and it shot out a recommendation.
Capital One: decent so long as you read the wording on the page. It'll suggest a bunch of cards but will tell you if you are preapproved or not on that page.
TL;DR: if the preapproval page gives you a firm APR and actually uses the word "preapproved," it's more likely that it'll lead to an approval. But those pages are not really the end-all because some people never get preapprovals and are still approved for some cards, while others will get a preapproval and end up getting declined.
