We started trying as soon as I got AF back (I told DH as soon as I went back to work but AF hadn't turned up by then).
My age had the biggest factor in timing. We then found out we had fertility issues we didn't with trying for DD.

I always wanted a nice two years....long enough have time with first bubs and enjoy her but not too long they wont be close enough in age to be good friends.....well that obviously didnt work out for us.
We will now have a 3 1/2yr age gap when this bubs is born.....and to be honest as time went on I was really ok with the age gap...I just hope the two of them still play together happily....

I agree with Lairdoz said though....depending on what your problem was, the choice between waiting for a 'better; age gap and the potential for not having another child at all...Id be jumping straight back into it....