To answer your question more completely:
I prefer front racks for a number of reasons:
1) They are more 'exotic' looking and I like that. I know this is a shallow reason but honestly, there are hundreds of rear racks out there and all but a handful of them look and perform nearly the same. Front racks have a lot more diversity, style, and interest.
2) Keep an eye on yer' stuff with a front rack. I like to be able to see what I'm carrying and make sure it is staying in place okay. I've had things fall off my rear rack before but I've yet to lose anything from one of my front racks.
3) Ability to run a much larger platform. While panniers are great for a lot of things, a platform can carry anything. Odd shaped and oversize items are not a problem with a large platform style front rack such as a CETMA or my second example above.
Now front racks do have some downsides:
1) Wonky handling with heavy loads. If you plan to use a 'platform' type front rack (as opposed to a low rider type with panniers) and you put much weight on it you'll see that your steering gets a little wonky. Not a big deal for a quick commute to work or the store but some people don't like it. Never bothers me but I've never run seriously heavy loads up there either.
2) Cost. Unless you own the tools to build your own front rack, you can expect to pay more for a front rack than for a comparable quality rear rack.
3) Selection. Again, if building your own rack the sky is the limit but if you are buying something off the shelf you'll find that there is not as vast a selection of front racks as there are rear types.