If I have someone to travel with I will usually just fix things as I go and not use a travel companies or go on a group trip. Except from trekking trips where I usually plan better and go in a group. If I go alone I usually also find some group trip.
I have used a couple of english travel companies I like (I am Norwegian not British). I went with Exodus Travel on the Goyko Ri & Everest Basecamp trip, the Chinese Wall trip and the Stok Kangri trip. They use local guides and all the guides on my trips have been really good. On two non trekking trips I have used Explore which I also like. They also use local guides and most of them have been great.
Recently I found this company which I have not used but which looks interesting (it is Norwegian): Nanook