If I'm reading correctly, you have 3 accounts opened in the past year - secured Platinum, QS1, and Fingerhut - and are working on keeping them all in good shape. That's definitely the right direction. I'm not sure you want to go apping around much right now, as your scores are still a bit low for the cards that won't kill you with fees and stuff (Credit One, etc). If you're wanting more unsecured credit, your best bet is probably to wait a while longer and let your perfect payment history and your three good accounts age a bit.
Capital One is acting a little less lenient lately, and so your limits may not grow as quick as you'd like them to, but they are still a solid lender who does tend to reward patience and patronage, and if you're looking for a car in a couple of years, their auto finance may be helpful too.
Discover may be another option in 6 months or so, once your score is up a bit and your history continues to improve - assuming of course that you did not burn them before. I don't know that you'd really benefit at this point with their secured IT, unless you just want to go that route; if it was me I'd wait for my file to warrant looking at the unsecured IT. Again, assuming you didn't burn them in your previous life.
Fingerhut is not a bad way to boost your rebuild, just be careful with them. Don't forget to buy some socks or something every once in a while, so they don't close you down and blast your utilization work to pieces. Also be careful with their "ghost" CLIS - they love to increase your limit by $500 or so, then if you don't spend that much before a certain date, your limit goes back down. Since their pricing is a bit high and their interest rate as well, most people wouldn't want to buy $500 just to "keep" the credit increase, but if you spend on other accounts using the Fingerhut to pad utilization, just be sure to pay everything else back down before the "ghost" increase disappears.
WIth your list of derogs, if it was me, I'd just quit applying for anything and work on those instead. Send PFD letters. Ask for settlement terms. Ask for deletions. Dispute things that aren't correct or are out of their time limit (if applicable). Those things are holding your score down more than anything else, and the points you could get back by working out those issues is going to be more than the few you might get from another card. I wouldn't be apping for anything, since when I got my score improved in a year or so, I'd want to be eligible for better cards from prime lenders - many of whom are known to be very picky about inquiries.
