Depends on what you are after...in my opinion the minifigs in the low rider are the better minifigs. The printing and detail on Quinn is great and I like the new batgirl cowl. Manbat and twins are pretty bland.
When it it comes to the build itself, the batmobile is better hands down. It is huge, much bigger than any batmobile that I have. The ability to raise and lower it are pretty cool to. It was more fun to build as well. The low rider has some neat components, but nothing great plus I've had issues with the wheels popping off and it not staying in the low rider postion
After buying and building them both, if I was told I had to keep one i'd keep the batmobile. Just my opinion, but you asked.