There's definitely no ideal, it has to suit you as a family.

I have a three year (and one day!) age gap between my first two (both boys). The pros were that we got to enjoy DS1 for a long time before his brother came along and he was TT'd. The cons (for us, not everyone is the same!) were that DS1 found it hard to adjust to not being an only child after being one for three years - he acted out which was really hard to deal with. They are now almost 4 and 7 and play pretty well together (they have their moments!), but DS2 and DD are 22 months apart in age and are great little friends. They play together really well. When DD came along, DS2 was still young and didn't struggle like his big brother did when he came along.

Again, every family is different and it will come down to individual personalities. We had a three year gap the first time because I just wasn't ready to have another one yet. The smaller age gap was because I wanted to hurry up and get the baby stuff out of the way haha!