i have a 19 month age gap between my ds's my patner asked when ds1 was 2 weeks old if we could have another, i told him we will think about it when he was one, on his first birthday i was a month utd with ds2, the age gap between the boys is great, we were realy happy with the 2, i think the fact that ds1 is and always has been a easy going child, nothing realy 'fazes' him, made it realy easy.
however, i now have a 13 month gap with my daughters, and it has been realy difficult as dd1 is still a baby herself and is extramly dependant, and 'clingy' she is slowly becoming better with dd2, but has quiet a few moments of screaming tantys if myself or df have dd2, and she suddenly decides that she wants us instead.
i think it depends on your little one and her 'outlook' so to speak. it dose get easier as time gose on, kids are prety resiliant and usualy adjust well to changed situations.
what ever your decission you make, it is your decission. i hope you find the answer thats right for you.