Smith shoulder press, seat straight or seat slightly angled?

[Wichard20]

sorry if this a noob question

Been using the smith for shoulder presses, i usually keep the seat straight up, but I was working in with someone today and he had it slightly angled. It actually felt more comfortable, now my question is which method is better and safer? I figure straight up is better since your probably using more muscles to control, but slightly angeled is safer. can someone fill me in?

[ITHURTZ]

On the smith I use the fixed 90 degree angle and lean back on it, our smith isnt up and down, it goes at a slight angle. On dumbells though I angle the seat back. MY shoulders are pretty well built, but I have always wondered how they would be if I did 90 degree..