Hi, I think it largely depends, on what your goals are. Overall best bet with good signup bonus: Chase Sapphire preferred. The signup bonus (after minimum spend) can become :
1)43000 United miles (roundtrip to Hawaii in coach),
2)43000 Hyatt points ( almost enough for 2 nights at their top properties)
3)430 dollars in cash
4)540 dollars for cruise , airfare or hotels.
Only you can decide, which option suits you best. Regardless, unless you
spend a ton on credit cards, your best bet is to regularly sign up for new cards with large
bonuses,which give at least 400 dollars in value upfront. Use your purchasing power toward minimum spend, if your credit score allows it and if you don't plan on getting a mortgage soon. This site and some others will have more info on this.