I did really well on my SAT subject tests but not too well on my actual SAT. Would colleges care if I sent just the ACT and SAT II tests or would they really want to see the SAT as well?
Send your better score in. No, they don’t prefer either test.
Check with the college, some require both. In most every case they will take the better of ACT or SAT scores.
Majority of colleges do not even use subject tests to determine admission. For those that do require, recommend or consider subject tests, you can do what you suggest except that for Yale, Georgetown, Stanford, and Penn, you must also send all SAT scores.