If you are going to be running outside it is best to get a pair of trainers that compliment your running Gait. You can get this checked at a store that has a gait running machine, which consists of a treadmill, camera and computer. This will allow the shop to recommend the best type of trainers for your gait to reduce injuries caused by road running.
If it is just for the gym, it don't matter what you get. Most gymwork is less invasive as outdoor running, so you can choose the type that look the best if you want.
I go road running between 20k - 30k a week, and I wear Asics, because they offered the best support for me.
Saying that, I have a few niggles so I will need to go and get my gait checked again. I will be going to Go Outdoors as they have machines in there.