Hi. This is a really hard decision to make! Putting a healthy dog through an op.
We've had four girls and always had them spayed after their first season. Our first died at eight so never suffered incontinence but the second one lived to thirteen and did. It seems to be easily treated with drops in the food. (The other two cockers haven't got to that age yet!)
Vets views vary, even within the same practice which makes the decision harder!
There is a belief that spaying at six months means you end up with an immature dog, emotionally and physically as they are still growing at this age. So it depends on what age they have their first season. Maddie was 15 months before her season so wasn't spayed until 18 months. Bramble was 9 months so spayed at one year. They are very, very different dogs but is that a result of early spaying... who knows?
Both dogs were supposed to have keyhole surgery, but Maddie then had to be cut further as her organs were small and in the wrong place. She then had a bleed. Bramble's was straightforward.
I tell myself that if I ever have another girl i will wait for two seasons.... at least the coat would stay nicer for longer!
Good luck with which ever you decide.