If you're looking for more, regular hours, then sticking to Reserve would seem to be your best bet. When I was on a shite contract I used to work in other DOs to make the hours up. As a Reserve you're probably going to be of more use to your DOm, helping him out when he can't sort his duty list out, and you'll therefore pick up more hours.
Downside of this is if you do make yourself TOO USEFUL you may never get a chance to move onto your own duty. Because the DOM will still want to use you as his personal fire service.
Depends what the turnover is like in your DO. Is it just a case of "Dead Man's Shoes",or do have a chance of Re-Signs on a more Regular Basis? Some DOs just NEVER seem to have a Resign. You might also like to think about taking the PT duty and then finding another job outside RM as well?