There isn't a "right" answer. A prelim surgery year would get you clinical experience, which would be good. And it won't create any funding problems, since you'd get 5 years of full funding after starting a prelim GS program. So that's all good.
But, a prelim GS program isn't going to have much free time in it. Getting enough time to go on interviews will be complicated. Residency, unlike medical school, is a job you're paid to do. You can't just take whatever time off you want. You might find that they insist that you use your vacation time to interview, and you might have trouble fitting enough interviews into the time you have. Plus, the critical issue if you do start an internship is that you do well -- is that going to happen in GS? Last, assuming the application timeline holds (which is anyone's guess at this point), you'll be submitting on Sept 15th which means all of your letters should be in by end August. That means that you'll have completed 1-2 blocks, at most, of your internship. It will be difficult to get any letter other than "heartonic started here and so far is doing fine".
But there are downsides to a non clinical year also.