amp or preamp most important

Tvad is correct. A bad preamp can screw up the sound but the best one will not make up for the deficiencies of the rest of the system.

Amplifier.

The best answer is that everything in the chain matters. I have been listening lately to a $16K amp with $4K speakers and those speakers sound so much better then they do with lesser amps that it can hardly be overstated. (Not that the $ means everything, but I am finding now that there are many rather expensive amplifiers that have qualities that no far less expensive amplifiers can match.)

In general "the preamp is more important that the amp" is one of the larger audio fallacies around. I'm not sure where it came from. It's flat-out untrue for me over the course of trying dozens of preamp/amp combos.

Totally agree with TVAD and it is much easier to screw up an amp purchase than a preamp purchase (for the most part). Having said that, both pale in comparison to the importance of the speaker (and room) in determing the overall sound and quality of your system. If you don't that right and to your liking, no preamp or amp is going to make that big a difference, not compared to the speaker and room.