Staying off site at the Best Western across the street from the park.
DLR is a little different than WDW. DLR has what they call "Good Neighbor" hotels and a large majority of people stay off property. So it's usually not a big deal to be off. Since you're within walking distance, that'll be great.
As far as the which park, if you really don't care about the "nostalgia" of being where Walt walked, then DCA is going to have more "unique" stuff. Disneyland is basically a little MK with a few unique rides. The castle is smaller, main street is smaller, it's far more crowded (especially in Adventureland). As others have mentioned, many of the DL versions of the MK rides, though, are much better like Pirates and Space Mountain.
But again, if you want a unique experience, DCA will be completely new for you. The two parks are right next to each other (some people don't realize they are literally a 2-3 minute walk away), so you can reasonably hop if you wanted, and I would recommend doing that, even for a first timer. Basically do the rides you know you love from MK over at DL and hit up the unique rides like Matterhorn and Indiana Jones and then hop over to DCA and do CA Screamin, check out Cars Land and do Radiator Racers.
Or as one person suggested, you may start at DCA, grab fastpasses for World of Color, ride Screamin and Radiator Racers, then hop over to DL until the evening and go back to DCA for World of Color.
If you don't want a hopper though, DL is the easy answer as you'll have more to do.