I don't have a definite answer for you (and I'm not sure that one really exists) but clinical vs. wetlab probably doesn't make a difference. I've heard some PhD's trash-talk clinical research because it's "easier" and "the results aren't as meaningful" but that's just prideful wetlab research opinion 🙂 Clinicians are likely to engage in clinical research over wetlab research, so I doubt they'll feel that one is more meaningful than the other. Your application will ultimately be considered by clinicians and not wetlab researchers, or so I'd imagine - so it shouldn't matter.
What does matter is that you have something to show for your work at the end of the experience. My wife did some clinical research between her first and second years of medical school, and from that she was given the opportunity to attend a number of conferences. She's done poster presentations and has even given an oral presentation. Those are things that can be talked up... and to think, all that from only a few months' worth of work! She was paired with an ambitious faculty member who wasn't new to working with medical students on research projects.
One of my wife's classmates did some wetlabbish work during the same period, with a different doctor (MD/PhD with a new lab). She was also able to present a poster and give an oral presentation about her work.
Looking further ahead, the research lab that I'm in (wetlab research) has a collaborative arrangement with a surgery department. The lab constantly has one surgical resident doing research, always for a two-year period. I presume that the residents take this position in an effort to make them more competitive for fellowships. The lab has some good success stories from that.
Ultimately, the outcome may be more important than the process, in this case (sad but true). Whether you want to do wetlab or clinical research, try to find a PI who will give you a project that can realistically be completed or heavily moved along in the time that you have. Even if you don't get a publication in that time period, if you provide meaningful contributions (and get the PI to like you) then you'll be listed on any publications stemming from that work and can point to them later.
Finally, be aware that many students seem to be taking a year off (usually between third and fourth year) to do research, if they're going to do basic science research. The number isn't so great right now, but I was surprised to find that it isn't a rarity (at least, not at this institution). So if you're looking to enter a really, really competitive field, there's a chance that summer research alone won't cut it (unless you're lucky and get a very fruitful project).
Congratulations on your acceptance to medical school, by the way - I hope to be in your position next year 🙂