I have 3.5 weeks to travel around, and I was thinking of going to Argentina/Uruguay/Brazil or some combination of two of the three (with Argentina being the most preferred).

Problem is, I know nothing about any of the three countries. Does anyone have any advice on itineraries I should look at?

Thanks

What time of year?

Late August and early September

If you want proper advice and tips that will be valuable to you, you need to do your homework and be specific.

Tell us what you enjoy (and what you don't enjoy is also useful), who you will travel with, what interests you have in the various categories of things you do when you travel, and also an approximate idea of what sort of budget travel you are looking at.

It is pretty easy to visit BA and various spots in Uruguay like Montevideo, Colonia, and Punta del Este by flying in to BA and traveling by ferry/bus. I'd recommend a trip to Iguazu Falls at some point on your journey, perhaps transiting from Brazil to Argentina that way.

Patagonia in Southern Argentina has some great places to visit, including Calafate and perhaps Ushuaia, though these are a long trip, perhaps best made by air.

I loved Bariloche and the mountain areas, which are doable by land transit from BA. I don't know if you could still go skiing there that late - the Argentinos can weigh in on that. Mendoza is a great place to spend some time enjoying wine tasting and trips up into the Andes; again, a trip, but doable by land from BA.

Argentina is a very large country with huge numbers of things to see and do.

Have fun! I wish I had that kind of time off....