We had booked our Argentinian side day trip through a tour company as it is hassle free and cheaper to do it this way compared to doing it by yourself. The whole trip was around $100 – $150 for three persons which included the bus fare, the entrance tickets to the Argentinian side of the falls and an English speaking guide. But if you somehow find a reliable way to do it by yourself then by all means go for it as the tour company is way too time consuming. As the tours are bus tours, the pickups while going to the Argentinian side and drop offs while coming back to the Brazilian side uses up a chunk of the time. Also once inside the falls we had to wait a couple for times for some people who wanted to do different activities inside the falls like the boat ride , etc.
80 % of the falls are in the Argentinian side. So to feel the actual might of the falls the Argentinian side is phenomenal. It has around 3 trails and it will take a whole day to cover all of them . We covered just one trail which was good enough and tiring enough. The Argentinian side is more spread out compared to the Brazilian side and involves quite a long hike no matter which trail you take. (By hike I mean just walking on the trails , not the typical hike). There is a toy train ride which is relaxing after the walk in the heat.