The best is both.
Small, dedicated, toilet with as little space as needed, just for a small washing basin. Here even common with just cold water and single tap.
Then a "combined" bathroom with lots of space.
If you are really bad, you will appreciate the rest of family does not need to watch you all the time. At same, you get two functional items available which can be used in parallel.
My rating is:
1) dedicated closet + combined bathroom
2) dedicated closet + simple bathroom (no toilet)
3) combined bathroom
I will take 2) any day over 3). But will never take 2) over 1) if there is a choice.