Since it will be the first, it may not matter much if it is full size or commander. Get the other size next.
I own 2 full size 1911s in 9mm and 45. I am dreaming of a bobtail commander or 4 inch in 9mm. I have not shot a commander/4 inch but handling one feels like it balances better for me.
If your plan is for carry, then get the bigger one first. This way, you will have more reason to get the smaller one in the future
If wanting to spend big bucks, I would go with full size.
Maybe it is just me but when I think 1911, it is a full sized 1911.