It's definitely got to be a personal decision. I don't think there's an 'ideal' age gap, because it depends on your circumstances and preferences.
I've got two boys, 17 months apart. They are now 22 months and 5 months. It's been hard work, definitely, as it's dealing with two lots of nappies, feeding, bathing etc. However, for me personally I don't particularly enjoy the 'baby' stage so know that in a few years, they will both be much more independent and we will have much more fun!
A friend of mine absolutely loves babies and has three children, with gaps of five years and six years. This suited her perfectly as she was able to dedicate herself entirely to each baby from birth until school age, without having to 'share' her time dealing with another baby.
As I said, it's got to be up to you; having two babies under the age of 2 is extremely draining, but if you love babies then why not?
Good luck whatever you decide!