I'm considering rmbp or dell xps/precision line. Which is better for music production overall. Any dealbreakers? i plan to buy a decent audio interface. Unbiased opinions please.
This, absolutely. Some software is either only available for or vastly superior on one OS (e.g. Logic on OS X, FL Studio on Windows).
If you're using Ableton or Pro Tools, either OS will be fine.
If you're an absolute beginner and have no previous experience with any music production software, I would give the edge to the rMBP since it comes with Garageband, and there isn't really any equivalent beginner software on Windows.