I'm old fashioned and prefer to have my "frame fit" pumps in front of my seat tubes. I never cared to have a pump under the top tube for lots of reasons... some aesthetic, some practical. On the practical side the pump always gets in the way when picking up the bike by the bars and top tube plus it's more easily knocked out unless it's strapped in place.
If I were going to ride some place where I needed multiple water bottles, then maybe I'd consider it (pump under the TT and 2nd H2O bottle on the seat tube). When I lived in the Southwest where it was hot and dry, I used to carry 3 bottles on long rides: one on the DT and 2 on the bars.
On the few bikes that I have with down tube H2O bottle mounts I put stainless steel button head screws in them to keep out gunk and water. They're almost flush so there's no interference with the pump.
verktyg
Chas.