As a truckie here's a little info...
Voyager - slots filled until 2016, none for re-treads any time soon although as an "ab-initio" you may well have a stab at this. Obviously the type rating is a massive plus, the junior crews haven't been getting a lot of flying recently
AFAIK and has a few issues but looks to be a good long-haul job sans face time in the next year or two.
A400 - Quite a few slots around ATM. The new boss has apparently said that this will be a face-time Sqn for the first few years whilst it is stood up. Nobody is sure what the actual job will entail but a lot of Brize mates are steering clear.
Herc - Rumour has moving to a fully tactical role once A400 takes on strat. Frames are busted so will need recovery time once Herrick role is complete.
C17 - Future is bright although continuing Herrick runs/det TFN. By the time you're through the OCU you'd hope that would be finished. Long haul type operations with a few more westward looking routes. A good bet
Sentinel - Slots available but extension only for five years post '15 (I think?). Lots of hours, good type rating.
Shadow - Certainly a marmite aircraft; some love it, some hate it. Detachments solidified now so fairly stable, just a lot of time away. Uncertain future.
BAE146 - 125 is chopped in April and the 146 losing 30% of its crews; don't expect any slots in the next few years.