Career opportunities: middle office of top investing bank vs. proprietary algorithmic trading

I have two offers, one is in model validation at risk group in top investment bank and the other is algorithmic/high frequency trader in proprietary trading company. I am wondering about career opportunities for both of the roles.

Since this will be my first job out of school, I wonder how much I can learn at each role and which would be the better career start. After reading other posts, it seems that moving from MO to FO is quite complicated, but I wonder if after gaining several years of experience at MO at top bank it is possible to FO positions in other banks or if such transition is equally hard as going to the FO in the same bank.
On the other hand, what are exit options from algorithmic/high frequency trading role. Is it possible to move to sell side FO after gaining experience in trading ideas development, or the only option is continuing similar work at other HF trading companies.

Any comments would be highly valuable!