Well, it depends on your background and interest, there is no right answer. Do you have experience building applications? Can you write MapReduce jobs and Pig Latin scripts? Are you familiar with Sqoop, Floom, etc? Then you are in a good position to move into a dev position.
On the other hand, if you want to essentially work as a sysadmin, then Hadoop admin would probably be more up your alley. If you'd rather spend your day setting up new Hadoop users, taking care of maintenance and support issues, and doing things like capacity planning, go the admin route.
You aren't going to go wrong either way. They are both good paying positions that are in demand.