Hi
I spent a year working in the Lembeh Straits and found I used both - and the wet lens too.
The 60mm is best for things like ghost pipefish and nudibrancs. The 105mm is ideal for pygmy seahorses and pygmy pipe dragons. It allows you to, as others have said, stay 2'-3' away and get your strobes in a good position. I did find though that the high-speed hunting of the VR 105 can be a bit much at times - and even lead to a feeling of seasickness! MF is necessary sometimes. Interestingly the slower hunting of the old 105 didn't cause the seasickness issue. I wonder if Nikon know?
Seahorses and pipe dragons can be very hard to find in the viewfinder with a 105. You might want to talk to the guide about him pointing to the seahorse with his stick so that you can can find the stick in your viewfinder and work down to the seahorse. Alternatively moving a little distance away from the fan, "find" the seahorse in your viewfinder and then gradually move in closer re-focussing all the time.
Patience and excellent buoyancy skills are the name of the game. And luck. Seahorses will turn away very quickly and that classic shot of them looking at you is very hard to catch.
The diving is sensational. You'll love it 60mm or 105mm - have fun! 