Hi ! what iPad is very good for my best studio Beatmaker 3 iPad 2018(6gen) or air 3 or maybe Pro?
Anyone of those will work. It’s up to your needs.
I have a 2017 base ipad and enjoyed it well enough for close to a couple years but on my newly obtained used 10.5 Pro I absolutely love it. The mixer and fx are super super snappy and I can get way more instances of synths. But yah, even on lower end ipads BM3 does work really well, especially if you are mostly in the sampler and use FX Aux sensibly.
Air 3 or Mini 5 look like they could be the new bench mark devices, they have modern CPU and headphone out.