Hard to know where to start.There is so much to do in Mad!
But you only have two weeks...so....
Probably best option is to start in Antananarivo (Tana). Take the taxi brousse to Andasibe, stay one night to see the incredible Indri in the rainforest plus a wealth of other Lemurs, Chameleons etc. Then back to Tana to take the taxi brousse down the RN7 going through the highlands. Stop at Fianarantsoa, take a car to Ranomafana, beautiful primary and secondary rainforest either doing a one day hike through the secondary forest or a two day, strenuous but incredible trip up to the primary forest, camping overnight.
From there, another taxi brousse to Ambalavao and from there take a day trip to Anja where you will see the famous ring tail lemurs and very few tourists.
From there, continuing along the RN7 (the only decent road in Madagascar) carry on to Isalo where you can spend a few days hiking through spectacular scenery. Back on the road to Tuliar and arrange a trip to Anakao to flake out on a beach for a few days.
Then, fly to Fort Dauphin where there are several more parks before heading back to Tana.
Alternatively you could fly north to Diego, take a tour to Ankarana to see the Tsingy and some Lemurs then head down to take the boat over to Nosy Be for a few days. Back to mainland and head off to Mahajunga then to Ampijoroa where the have a dry forest, loads of Lemurs and an incredible canyon before taking the taxi brousse back to Tana.
First is the most popular option, second is my favoured choice but be prepared for some very long, very uncomfortable taxi brousse rides, unless of course you could afford to fly!
You dont need a tour operator to do most of this but guides are compulsory in the parks
Let me know what your final itinerary will be and I shall give you any tips I can, places to stay, taxi numbers, where to get the bus, best guides etc.