underwater? A fisheye lens!
Lol... Sorry!
I have both lenses, and to be honest I do not really care for the 14mm 2.5. The other thing you want to consider is the fact that when you are under water you will want to use a lower f-stop to gather more light. So for me I would choose the 20mm 1.7. If you want to purchase the 14mm 2.5 I would be glad to sell you mine :-).
Best Regards
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