Cars, definitely. Space Mountain. GotG, some of the bigger e-tickets obviously. It all depends on where you want to start first. When I go, we kind of go all over the place. Maybe 3-4 rides in DL first and then depending on how long we have to wait (always with FP/MP, never in standby lines unless the posted wait time is 15 or less) and then hop over to the other park for another big e-ticket ride. Last time we went with a magic morning extra hour we did about 4 or 5 rides before we started to see more crowds pour in. Once it started getting busier, we sat down for breakfast at an "off" time (aka a time when people aren't naturally getting hungry or eating when they considering breakfast, lunch, dinner time) and then went from there. I would try to get a FP for rides like Space Mountain, Cars, Toy Story Midway Mania, and Guardians (though Guardians doesn't tend to run out that much). The former tends to run out pretty easily depending on the day/which passes are unblocked, so try to get to those ones first. I don't think you should have too much of a problem getting FPs for any other rides.
A lot of it depends on what your personal preferences are. Every group is going to be different. For instance, it's me and my friend usually when we go and it's usually 5 days at the park. We have lots of time there and are in no rush to get everything done in one day. But for your one day trip, I'd say get on the biggest e-ticket attractions first, eat/relax during the busiest times (even pushing things a half an hour later can make a difference) like during parades unless there's one you guys absolutely want to see, and that will maximize the time you have for rides.
But to maximize your chance at getting onto the bigger rides that run out of fastpasses the quickest, I'd say hit them up in this order:
1. Radiator Springs Racers**
2. Toy Story Midway Mania**
3. Guardians of the Galaxy
4. Space Mountain (though this one you probably shouldn't have a problem with getting a FP even into the late afternoon)
**These will run out of FPs faster than any other rides between both parks. In addition to that, they tend to have the longest standby wait times, so it's not worth it to go on the rides if you're just going to stand in them for over an hour or two. You'll lose precious time getting on other rides, so get them while they're hot!
Other than that, you shouldn't have too much trouble with any other rides. I'd say head over to DCA first, get a few of the bigger e-tickets in and then head on over to DL to get a Space Mountain fast pass next, then go from there.