You can do the math - look at the rather few number of HM squadrons that operate that aircraft - and HC-4 of course.
The MH-53E series is a maintenance intensive aircraft - always has been since day one. When I was an instructor at HT-18, my peers who felew 53's typically had the lowest flight time - The number of squadron pilots to avaoilable/flyable aircraft was high so people were always scrambling to even make their 100 hours/year.
Your best bet is to track towards an H-60 - HC, HS, HSL. HM will go away since the MH-60S will pick up the mine mission and the HC and HS communities will merge with the HSC concept.
If I had it to do over again I'd go HS. All the action is around the carrier - your best bet of seeing combat and tracking career wise is being deployed with a squadron where you can be in contact and visable to your senior leadership. The whole Det concept is really not good for getting ahead IMHO. Also HSL and HC are less likely to be actually deployed in a combat environment.
My two cents...