Most of the shoots that I attend the 25 yd. targets are not bullseyes but small animal heads, stars, etc. about an inch in size and with some areas that if hit have a minus score. At 50 the NMLRA bull is 2 3/4" and the buffalo target ,that's usually used at 100, has a 5 3/4" bull.
For practice, an inch, 2" and 5" are good. This is all offhand from the pouch, some bring a small folding table to use.