Hi november,
The answer partly depends on what is your priority to achieve.The advantage of pns is that it will give you more certainty in what you will get for the rest of your life, ie, approximately €475 pa additional pension for every years purchased plus an extra€1425 on the lump sum. This is based on your salary of €38000 as your allowance is non pensionable. Based on the info above you could purchase up to about 12 years. The cost is not cheap. You can get tax relief based on the full income of €58000 - 35% now and 40% from age 60, I think. Your HR/Salary Department should be able to give you a quote for the cost of pns purchase.
The advantage of an AVC is that you can use the fund much more flexibly. Example. If you retire at 65 with 27 years service, your current occupational tax free from lump sum will be about €38000. However, Revenue rules should allow a lump sum of up to €87000 (58k*1.5). So you could take an additional €49000 from an AVC pot. Any left over could be invested in an ARF, which you can draw down flexibly. However, unlike the pns option, there is no guaranteed annual income for life (beyond what is in the ARF).
Put crudely, the pns route may give a better financial return(with less flexibility) if you live long into retirement.It is guaranteed, so it may provide some peace of mind in this regard. If you have a shorter survival span, the AVC may give more financially - as well as more flexibility on how you use it.
If you go the AVC route you can opt for a conventional AVC or a PRSA AVC. Beware that returns on your AVCs are based on investment performance. The Pensions Authority have a booklet on these options, which you may find useful:
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Best of luck. The above is my take on it. I am not a pensions expert!
EDIT: Is it certain that the allowance is not pensionable ? Why not?