First of all, CONGRATS!
Now.. here it comes. You'll get alot of opinions on what you should bid as a NH. Here's my take as a 756FO about to leave to the 78.
The 756 will give you a variety of flying that you won't see on any other fleet. Also, with the amount of projected hiring in the future (take that with grain of salt) you will not be on the bottom of the list for very long. Sure, you MAY get a line sooner on the 73/Guppy~Airbus/Fiffy but it's probably only a few months difference. People can argue that IF you go to one of those, your (potential) upgrade will be easier in a year or two. But mind you, if you choose to be one of those Y2Capts in the future, you will be on RESERVE for a long long time.
(Please don't be one of those guys who wants to see an LOA changing the Reserve Rules [in the future] as we need a FULL Contract.. no more damn LOA's/MOU's)
On option would be to choose the smaller plane and then switch to the 756 in a year or two. It all comes down to how much you love/hate/don't mind training.
As someone who picked the 756 out of InDoc, I have had no regrets. Bigger cockpits with different types of flying and rare to have more than 2 legs a day.
Either way, enjoy the excitement of being a new hire and take it all in. Both the good and the bad.
See ya on the line~
Always
Motch
PS) No matter what, make sure you FS, FP & FtC