I've seen more and more choose to wait until after at least one heat cycle. I'd be inclined to follow the crowd on this particular issue. There are SO many variable in the equation, nothing really concrete can be nailed down as to the pros and cons of early/late spaying. I could conjure arguments for both with my limited knowledge. However my gut says that letting nature do "it's thing" and wrought a fully intact female before the snip-snip makes more sense than changing the plumbing before the build is done. That's me tho and I am not an expert on hormonal/structure/bio chem in the least.
Never cook bacon while naked.