If you plan to remove the antenna a lot, then the BNC is better. I mostly use my 436HP at home attached to an outside antenna. When I travel, I often take it with me and use the Radio Shack antenna (same as the Remtronix) BNC version.
The BNC adapter on the 436HP will stand up to repeated removal cycles better than a SMA. It's also easily replaceable if something happens to it. Using the SMA fitting will mean a trip to Uniden for repair if something happens to that.
So, how you plan to use the scanner will decide which version you want.