I currently own 4 merc 4 strokes, a 175 verado, 9.9 pro kicker, a 20 and 25. All run great and would have no problem buying another merc..... I have had 2 issues with the verado, but it is 12 years old. No issues with the other 3. I had more issues with my last Yamaha in the 6 years that I owned it. As far as being cold blooded, the 2 that are efi start quicker than my cars. The 9.9 can be a little cold blooded, the 20 horse starts a little hard the first time every year, but no problems after that. Out of the 2 that you mentioned, I would go with the mercury for sure.