To answer your question in the spirit in which it was asked: All things being equal.... (which they never are) the pre-amp will have a more dominant affect on the sound you get. (this answer comes from my experience and reading the words of those more experienced)
When I purchased an integrated a few years ago, I got a highly recommended piece in which the pre section was weaker than the amp section. When I went to upgrade, it made the process much more difficult, I couldn't just add a better power amp when the funds were available, I had to replace the pre, then soon after get a power amp (or look at 2 front end pieces!)
The conventional wisdom is: START UPSTREAM, that is; closest to the source. Get the best pre you can and add on from there. A good pre will make a mediocre amp sound better. A bad pre will make a good amp sound worse.
When I purchased an integrated a few years ago, I got a highly recommended piece in which the pre section was weaker than the amp section. When I went to upgrade, it made the process much more difficult, I couldn't just add a better power amp when the funds were available, I had to replace the pre, then soon after get a power amp (or look at 2 front end pieces!)
The conventional wisdom is: START UPSTREAM, that is; closest to the source. Get the best pre you can and add on from there. A good pre will make a mediocre amp sound better. A bad pre will make a good amp sound worse.