I think it depends what you like doing and what your circumstances are.
Ramblers Holidays has a good range in the area you are thinking of visiting but I've found their accommodation to be a bit on the basic side and I've frequently been frustrated that there are no single rooms available. This might not matter to you - you may be willing to share or you may get lucky.
I always find Explore have very good varied itineraries - usually a good mix of walking and seeing things. They are getting to be a bit expensive though.
Walks Worldwide are an interesting company. They have some unusual itineraries - Armenia, the Carpathians etc.
Mountain Kingdoms and KE Adventure are excellent in the really mountainous regions, being very experienced in initially providing trekking or climbing holidays in the Greater Ranges.
However, watch the single supplement if you reqest a single room, whoever you go with. One or two companies are guilty of charging for THREE accommodation places.:- Your own, the other half of your room/tent that no one is occupying plus the other half of the room/tent that someone else is occupying who did not ask for, nor will be charged for, a single. Sorry, that latter is rather difficult to explain. One company was quite open about this with me when I queried the "single supplement" charge which was obviously exhorbitant.
Anyway - good luck with whoever you choose and have a great holiday.