I would not go for fixed. Interest rates will probably not rise enough in the next five years to justify the higher fixed rate. If you can, go for a lifetime tracker with no repayment penalty. That way, if rates start going up, you can switch to a fixed rate product then.
I agree with flatbread...this is the best as you can take advantage of the current interest rates with the peace of mind that if they go up you can fix at any time.
However, if you are really wanting to have a fixed rate, I would go for the 3 year option as I think 5 years is too long to wait to review your mortgage. After 3 years you may feel comfortable with a tracker or there may be better deals out there.
Hope this helps and HUGE congratulations on getting your offer accepted on your house!
Depends how comfortable your monthly repayments would be if they went beyond 5%. If the answer is 'we'd be stuffed' I'd say go for fixed the 5 year fixed rate as being able to sleep at night is important. However, if you think you can easily afford to take the highs with the lows, I'd agree with flatbread and go with a tracker. It does seem a shame not to take advantage of such low interest rates at the moment. Good luck!
We ummed and ahhed about this for ages - didn't go for the fix in the end in our case. My slight concern though is that if rates do start to rise (and surely they must) then the banks will be well ahead of us and will have bunged up their rates on fixed rate products by then. It's a toughie.