I consider 2-3 years a good age gap, only if you feel like chasing a toddler around while you have a baby.
My oldest and middle child are 5 years apart, they are opposite sexes and I never thought they would get along, let alone have anything in common, but I was wrong. Tim (he's

was always trying to keep up with what Lindsey (she's 13) was doing, he never wanted to play with his baby brother, Tyler (he's 6). Now Tim and Tyler play together more because they do "boy" things, cars, wrestling, you name it.
Lindsey and Tyler get along the best, because at 7 years older then him, she likes to mother him.