Re: Flights -
If Delta is your primary carrier, you're best off accumulating points for Skyteam
airlines. Korean is an Ultimate Rewards transfer partner. Quite a few are SPG partners. If you accumulate points and transfer them to a Skyteam partner, you'll have a decent change of finding an itinerary that originates from your home airport on Delta.
And, to be blunt, Delta has a POS award chart. You're often better off redeeming on partners anyway.
As samhradh said, the best way to approach an award redemption, if you have a destination in mind, is to start with the destination. Figure out who flies there and accumulate and redeem points in the best program for your destination. Star Alliance is awesome for Asia and Europe. Oneworld is great for the Middle East and Australia. Skyteam isn't particularly attractive for any regions, but has a few hot spots like Korea. Don't worry about the specific airline so much. You can always combine partner flights into a single itinerary (although there are different rules for different carriers). By way of example, this summer, we're flying United, All Nippon, Air China, Asiana, Turkish, and Air Canada using US Airways miles. Last year, we flew United, US Airways, Swiss, and Air Canada using United Miles.
Marriott points aren't great for airline transfers. It takes 112,000 Marriott points to get 50,000 United Miles. All other airlines require 140,000 points for the same.
Finally, if you find an awesome redemption that originates at a different airport - EWR/JFK or SFO, for example - and you can find a cheap flight to get you there, don't be afraid to pay for the cheap flight and start your trip somewhere else.
Re: Hotels -
You're lucky enough to travel for business. That's a great opportunity to collect points and status. I suggest trying to stick to a single hotel chain on your business trips. Stock up as many points as you can and redeem them for your hotel stay on your vacation. Elite status also helps - Marriott Gold comes with room upgrades so you can redeem points for a normal room and get a suite. Don't forget to double up on your hotel stays. Big chains offer airline miles for stays in addition to hotel points.
Also, if you want to go somewhere interesting, don't count on large chain hotels. You can hack Priceline to get some killer deals on local joints.
tl;dr - start with your destination, figure out what points you need for the trip you want, stock up on those points.
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