I've tried all three. The portable units are a waste of money. They simply don't work well and are inefficient. The window mount units are ok, but a big enough one to both heat and cool are close to the same price as a mini split and you are bringing in outside air which kind of negates the use of C02 as you'll be exchanging and replacing your inside air (and wasting your C02). If you can install it yourself you can save quite a bit on the mini split overall cost. It's not difficult and the proper tools and gauges are cheaper than an install unless you have a buddy in the HVAC business. They also make units that are made to DIY install yourself and the lines are pre vacuumed. All the mini splits come pre charged. They are also very efficient for both heating and cooling, The DC inverter variable speed compressors use a fraction of the power of older heat pumps and AC units and have higher seer ratings. You can also get multi zone units that have one outside evaporator unit and 2 or more inside air handlers than can in the same or different rooms. I installed mine myself and working alone it was fairly simple 1 day process taking my time.