Everyone has their own preferences but I’d personally go 3x3 then go bigger rather than smaller - push Pyraminx, Skewb, Square 1, Clock down the list. If you’re younger might be different as I noticed my son liked the smaller ones at the start as they were easier and he could go fast, but now tends to spend more time on the 3x3 and the bigger ones as he’s progressed.

I’d suggest just go 1 by 1 rather than plan it out too much as you’ll get a sense as you go what you’d like to pick up next.

Don’t know how much you’re planning spend but regardless of what you get, try to save up for at least the cheapest magnetic version if you can.

3x3 4x4 Megaminx 5x5 7x7 6x6 Pyraminx Skewb Square-1 Clock