Mendoza - LOVED the Alta Montaña day tour (note that if you have a car you can just drive the same route as the tour; it goes up to the Chilean border stopping in various small towns, diques, viewspots, Puente de las Incas, etc. and you can stay up there for a night, maybe in Uspallata?). I got sick so I didn't get to do any wine tasting
I was there in November too and it was very hot but not so bad heading up the mountain. I didn't drive in Mendoza.
Bariloche - I went last year in Feb. and we rented a car and went up to San Martin de Los Andes... I prefer Bariloche because I'm a city-person and it's just more open, in terms of not being squished in between two hills (a bit reminiscent of Como Italy but smaller). But if you go to San Martin definitely take the boat for the day (or drive around the lake 30 min.) to Quila Quina for swimming and kayaking or rowing around. Also there is a drive up to a very pretty view spot but that road is treacherous. The road from SMA to Bariloche is crazy too, a large swath of it is unpaved. So pee ahead of time. To be honest, I was disappointed by the Ruta de 7 Lagos! The prettiest places were at both ends of the journey. Yeah there were a few really pretty lookouts but it was just lake after lake after lake after viewspot etc. And all the people we saw biking looked REALLY tired and with a bunch of dust and car exhaust in their faces. Maybe if you want to camp for a night in a peaceful spot, it's useful for that.
Villa La Angostura; never really got off the main street (which I thought didn't have much character) besides to go to the port and get the boat to the Bosques Arrayanes. Totally worth it!!! but what was not worth it was the walk all the way something like 12km back to the port... the pretty trees are only on the tip of the peninsula anyway and then it's just regular forest. it would have been fine if someone told us that the last part of the trail coming back to the port was closed off; we had to take an alternative trail that was very difficult and by that time we were nearly out of water; it was stressful.
Bariloche; love this place. Definitely head along the Circuito Chico and stop at the lift for Cerro Campanario - the best viewspot of them all!!! And then continue on to Llao Llao; spoil yourselves with lunch or a drink at the hotel (or a spa day which my friend did but I didn't because it was 1200 pesos) and continue on to the Swiss Colony for a tea or shopping in the cute stores full of hand made goods.... LOVED Circuito Chico and the Llao Llao Peninsula!!
I'm actually going back this year in Feb. to the area south of Bariloche that I missed: El Bolson (Lago Poelho) which is 2 hours south and Los Alerces Nat'l Park outside of Esquel which is another 2 hours south of that. If you have the time, both are supposed to be really great also.
If you aren't going to SMA/ Ruta de 7 Lagos, I would say you really don't need a car unless you want more independence and flexibility. You can go to Bosques Arrayanes on a tour from Bariloche that takes a ferry boat to Isla Victoria and then the Bosques. You can bus around Circuito Chico. Bolson is really small and there are a bunch of hikes directly from the town. Esquel you can get a day tour or get a transfer to camp in the National Park. The only reason we got a car was so that we could do the 7 lakes route and stop where we pleased. The day trips that drop people in SMA leave really early and its up and down up and down off the bus to take photos with a big group of other tourists. I was with a friend who was pretty high maintenance so for that reason it was better that we rented a car, but if you stay in a convenient spot in Bariloche, all the things I mentioned are easily accessed by bus or tour.
PM me if you have any more questions about anything I mentioned!