If you are planning to spend $25,000, then that will give you 25,000 miles on any airline of your choice (most airlines have credit cards that give you 1 mile per dollar). Some have higher-end cards that give you 2 miles per dollar, with an annual fee that is waived for the first year.

Since you mentioned Southwest, their credit card (through Chase) gives you 25,000 points after first purchase, and 1 point per dollar, which means you would end up with 50,000 points, which would be worth over $800 in Southwest flights. Other airlines would have similar programs, some better and some worse.

If you just want to go the cash route, then Capital One cash rewards will give you 1.5% of your total spending, or $375.

Do note that credit cards have monthly limits, so you would need to spread out this spending over several months.

Congratulations on your wedding