My suggestion would be for the Amazon credit builder card...if you're an Amazon shopper. After 7 on time payments it can get converted from secured to unsecured card. It's reports within about 2 weeks, from account opening, on your credit report. Not sure of min or max deposit so you will have to look at up.
Grab a self lender loan. Simple. Easy. Effective. There is no way a score is going to go up fast. It takes time. And depends what baddies lie in the background to stunt the growth. The time it took for things to go bad. Takes twice as long to recover most of the time.
Going from 596 to 700 may be very quick or rather slow depending why you are at 596. If it's due to lack of accounts, you can improve your scores rapidly, but if you have derogatory items, it will go slower unless/until you get those items removed.
I thought I saw that Amazon backed off the secured store card, due to complaints from politicians that it was "predatory." If it's still available, it's a great option for anyone who shops much at Amazon, because you get a 5% discount if you are a Prime member.
Otherwise, I suggest checking prequalifications with Discover and Capital One. If you prequalify for any Discover card including the secured card, I recommend grabbing it. Discover is great, and the secured card can graduate to unsecured after seven statements. With Capital One, the best thing to get would be Platinum unsecured, because it can be product-changed to QuickSilver down the road. The Platinum secured card is not as desirable because it will never graduate.
If you do not prequalify for any of the above, you could get an Open Sky card for now, and try again in two or three months.
I do not suggest getting more than two or three cards for now unless you have a specific well-thought-out reason to do so. Loading up on secured cards will limit what you can do in six months.
I would also seriously consider a Self Lender secured installment loan.
I think your on the right path and asking the right questions but also think you need to realize that gaining 100 points in a relativly short amount of time may set you up for dissapointment in the long run. I noticed you mentioned having a charge off in another post with BoA. How long ago was that? Also how many inquires do you currently have? I'm not saying 100 points in a year is impossible, but it's not exactly easy either depending on your credit background either.
Back to topic of a credit buidling loan. Self Lender as I said is easy to do. And once its paid you get the money! Cant go wrong. And it will count in the FICO bonus once 3 cards are established in time. But if you have a mortgage, car payments or any type of other loans already. It wont do any good really. Only need 1 loan to be effective.