What is my best pension option?

obriend6

I am a 23 year old earning 33,500 a year with guaranteed 4,500 in a bonus.
I have decided that now is a good time to start investing in my pension.
I receive a company contribution of 5% on top of the 1.5% i will contribute to my pension. I am Irish and plan to move back there in 5 years time.

So i have 2 pension questions?
1) Considering my circumstances should i opt out of S2P. If i will only be contributing for only 5 years is it worth staying in?

2) If I work for 5 years in the UK and lets just say 30 years in Ireland then which government pays my state pension. Will it be a combination of the two governments? Am i loosing out due to this circumstance?

Thanks in advance for the help