The best strategy is to sign up for new credit cards, meet the minimum spend requirement to get the signup bonus, then cancel them before the end of the fee-free year.

Consider that a typical card (Chase Sapphire Preferred, noted in earlier post) might give you 40,000 points for signing up, the same as spending $25-$30,000 with a lot of the spend in bonus categories.

In order to do that, you have to (a) have a good enough credit rating to handle it; (b) be willing to do the paperwork and recordkeeping, and (c) be able to spend (or manufacture the spend) to meet the minimum requirements.

If you do that, you can accrue fairly large amounts of all types of points and miles - although I'm not going to say if it's "hundreds of thousands" or "millions."

If the choice is cashback or points, then I'd say:

a) The best cashback card give 2%
b) 2 cents per point is more than most miles or hotel points will be worth, unless you redeem for international business-class travel or very high-end hotels.
c) You are usually not going to get big "signup bonuses." You may get decent quasi-cash point bonuses with some Capital One cards, but no "2% cashback" card is going to give you 40,000 points, worth $800, for signing up.

I've personally earned between 1 and 1.5 million points/miles in the past 18 months. But I have a wife who lets me use her name and doesn't interfere, we both have great credit scores, I don't mind keeping track of this stuff, and we spend enough (real and "manufactured") to make it all work. Some of the "manufactured spend" tricks require working capital - like you might have $5000 or $10000 floating around between accounts.

Not knowing your actual situation, I can't make a recommendation.