If the chain on the 10 speed is wider, go with a 10 speed. If the chain width is the same then I really see no difference.
I'm not really sold on even the 10 speed. More cogs you have, the narrower the chain. And with it, shorter life span of the chain. My SRAM chain didn't even last a season and replaced it with Ultegra. And I don't race. Just a casual weekend rider these days.
For my casual riding and training on hills with 10% grade, I rarely use the top two cogs anyway. I only use 8 cogs in the rear.