Both are good scanners, but you'll probably get more useful answers by asking your question in a local forum where folks are using those models to monitor systems in your area. As for audio drop-outs on the 396XT, I don't have that problem in my area. This may be because I'm not using a feature that causes the drop-outs for other people.
Plus, there's a lot more to consider than a single issue. For example, I prefer the smaller physical size, memory design, and GPS capabilities of the 396XT. Also, any opinions you get regarding P25 performance of an XT model will be out of date in the next few days. Uniden recently announced a firmware update that is designed to improve P25 decoding, and it's slated to be available by the end of the month. That update alone could change everything. Good luck on your decision...
ScanCHS