I climbed Aconcagua with Aventuras Patagonicas in 2005. They were the first guide service I ever used for climbing. They specialize in Aconcagua and it showed. It was such a relief not to have to deal with the logistics of food, transportation, permits, burros, etc. I was actually planning on trying the Polish Glacier route but we had an episode of vento blanca at our 17,000ft camp that dumped a hugh amount of fresh snow on that route and then had some members have to descend due to altitude losing one of the guides. The Vacas valley route is the way to go. You don't have to deal with the hordes of people going up from Plaza de Mulas. By doing this route you end up circumnavigating the whole mountain and seeing all sides. You descend through Plaza de Mulas and can see why hiking up that route would be a drag. By going through the Vacas valley it also allows you to acclimatize better. I can highly recommend them. Remember the peak season is Dec-Feb. It's their summer and it can be fairly warm on the hike in. We had a couple from New Jersey on the team that had a terrible time with the heat.
I made a trekking to Plaza de Mulas in 2017 with Aconcagua Mountain Guides and this summer I joined one of their expeditions. Both experiences were great. Most of my group summited on January, after struggling with the weather. The food was great, the basecamp had good services and, above all else, their guides were very professional and experienced. They waited for the right time to push for the summit and we made it because their knowledge of the whole climbing scenario. Lots of things to do back in Mendoza, especially if you’re interested in wine tours. We went to Iguazu falls after the climb. Also beautiful.