A question a lot of people wonder is who plays what horn and also the related, larger question of what is a professional quality horn? My standard answer is a professional quality horn is a horn that a professional would seriously consider playing. In other words, it is not something determined by marketing but by the market.
When you purchase a horn you want to buy a horn a professional would seriously consider playing. Jeffrey Agrell of the University of Iowa has put together a great resource on the topic of professional players and the horns they play. The list is here; you could get lost in this list for ages pondering the many makes and models. He also offers this quote from Paul Navarro which puts elements of the list into context.
As you look at who plays what in whatever section, it is important to consider that the instrument chosen by a particular player just might not be the instrument that the player likes the best out of all of the instruments available.
Some of the considerations that may influence what instrument is chosen to use may include: (not in order of importance)
+the principal’s preference
+the conductor’s preference
+what works best within their section
+what works best with the acoustics of the hall
+repertoire considerations- especially for chamber orchestras
Above all a pro wants a horn that produces a professional sound that fits with the work situation where you are at. In particular note that a horn that fits in well in Europe may not fit in well in the USA and also the horn that is very American in character won’t fit in well overseas.
In terms of me, for over ten years my personal, go to horn was the big Paxman 25A in the photo above (similar to a Kruspe but with the Paxman wrap) but UPDATE: I have switched recently over to a Geyer style custom horn. I have a few more thoughts on recommended horns and mouthpieces here. And also check out the Agrell list and his site in general, this is a massive resource on the horn.
UPDATE: Also check this article on the topic Kruspe or Geyer for more background.