I've been hiking 2K peaks all the 12 months of the year, and july and august are the most crowded months, by good margin. I've been both to Trollheimen and Jotunheimen. There are people at both places, so that is not the biggest diffrence. The climate in Jotunheimen is more alpine, with colder weather, more rocks and snow/ice (higher terrain = colder weather).
You can se valleys, peaks, snow and glaciers watever route you choose, nothing more or less..... , The peaks you have choosen are quite easy to reach, you just need to be in a normal physical condition..
Good luck, and have a nice trip