For small runs, you can use anything...6061 is the cheapest, and will be fine for test runs or a few thousand parts. But it's gummy, so clearing the chips is critical. 7075 is harder (machines nicer), so it will last a lot longer, but it's 2-3 times the price. QC-10 transfers heat better so it's better for larger volumes.
You will likely be frustrated with a Taig. Get the heaviest machine you can afford, even if it's used. In machines, heavy typically means more rigidity, which is better overall.