Hi andreas,

i think you can go either way.

i have boats that are both varnish finished and paint finished. 

a scratch shows more when it cuts through a layer to a different color (e.g. deeper) and when you have more of them.     it also shows more when it is on the part of the boat you see more (sides and deck).   so for whatever its worth, i don't usually worry about the optics of the bottom.  i do try to be careful but it's boat to be used and enjoyed....and boats that get used will get their bottom scratched.

the only think i would add is, overtime, it is easier to visually remove scratches from paint.  the reason for this is inevitably, on the bottom of a boat, you will get a deep scratch that goes into the fiberglass, and the repair, will require some glass work.  and it's hard to make these glass work repairs  all blend in perfectly and they will be seen through the varnish.   with paint, once you are done with the repair, the paint completely hides the underlying scratch.

the good news, also, is when scratches get bad on your own boat and you want it to look new again, you can totally refinish it in a way that is pretty impossible for a store-bought boat.

the picture below is my ten year old night-heron all varnished.  every year i took care of minor scratches on the bottom. just a days work at the end of season before putting it away for the winter.   after 8 years it had a complete refinish and was prettier then the day i first launched it.

notice, you don't see the bottom:)

hope this helps.

   When someone askes me that question I usually say, " I built it I can fix it".   I have some painted and varnished boats. I try not to scratch them, but it happens. Paint can patch easy if the paint on the boat hasn't sun faded. Same with varnish. I'd say to put the color on that makes you happy. If you like the blue paint blue. If you like the varnish, then varnish.  As for everyone else just keep the boat moving and they'll never know. 

Thanks

useful thoughts

I will post a photo when complete