Depends on what do you need, what kind of lineup you're using.

Okay let's look at it this way: With 6p naruto and sus kakashi lineup, you'll be basically unstoppable given that you are faster. BUT, susanoo kakashi is a one trick ninja. His only redeeming quality is his passive; which to me is kind of not worth his price. Edo itachi, on the other hand, is an overall great support ninja with both c.c. and anti-c.c. qualities, ability to cancel buffs, and relatively safe from being chased as well as allowing you to survive most round 1 blitzes. I may seem biased but I would highly recommend you to get edo itachi over susanoo kakashi. You can still stomp people with 6p naruto even without susanoo kakashi.

But well in the end it's still up to you. Consider your options carefully