It's really hard to generally say what points program is the best, since it's based on so many factors like annual spend, points bonuses, who you fly the most, who you plan on flying with in the future, first/business vs coach redemption, etc. I assume you are looking for a points-based redemption instead of a cash-based redemption program.
I personally value AmEx Membership rewards more than Chase UR since they transfer to many different airlines (main exception is United). That being said, you already have a Chase Freedom, so you can just accumulate points and build credit for now. When you want to redeem for miles, then you can get the Sapphire Preferred and be able to do that.
WRT using Membership Rewards for stuff like ipads, you can do this, but I wouldn't bother as I value miles higher than cash redemption. If you do go this route, it's usually a lot better to use MR to buy giftcards for like Best Buy and then buy an ipad, as the MR store is grossly overvalued.
Additionally, why not have both? You said that your credit isn't good enough to get AmEx, so I wouldn't bother now. But there's nothing stopping you in the future. Build credit and get an AmEx with a bonus offer to maximize your rewards. Or if you can qualify for Zync now, get that and start earning MR points, and then get a gold later so you can transfer them.
Finally, I would start reading rewards travel blogs, such as view from the wing or thepointsguy. Most are pretty baller (consultants and the like) but lots of great info on benefits, perks, spend requirements, etc. Flyertalk forums are also good but it is seriously a lot of info to comprehend and more to do with maximizing redemptions than earning them.
LIMITS IN CARD DESCRIPTIONS