IIB offer interest only for up to 36 months during the term, PTSB offer a 6 month initial payment holiday - both lenders have their merits so why not approach both for approval in principle and decide from there.
Frist Active also tend to lend more. They do 100% mortgages and they also include room rental (no minimum earnings required). They do not do deferred payments but the max LTV for PTSBs Take 4 is 98%.
You should check out EBS as well - I think they lend more than IIB. They also have an easy steps option for the first year where you pay 85% of the monthly repayments.
No problem Pexus, I would expect IIB to lend more than PTSB as they take in room rental which can add upto 30k onto the amount you qualify for. Also, if you are willing to take a 3 year fixed rate they may lend a little more...