is worth playing mf when you have graves?

{quoted}

http://orig09.deviantart.net/9043/f/2012/016/e/8/lol___mafia_miss_fortune_by_knockwurst-d4mlns2.jpg

That should be reason enough.

Miss Fortune has two main advantages over Graves.

1. Her ultimate has apply Black Cleaver stacks to entire teams.
2. Her W passive causes her autoattacks, Q, and ultimate to apply on-hit AD-scaling magic damage.

These give Miss Fortune an advantage on AD-heavy teams due to amplifying the damage of your allies and reducing the effectiveness of armor against you.

While these aren't massive advantages, they do help. Especially in soloqueue where you can have an AD top, mid, and jungler due to poor communication or people not adapting to your team composition.

but graves has an escape and is a better lane bully with a much better late game

Well put, and I hadn't considered that. Would you make a post like this over on my discussion right over here?

{quoted}

graves beats her in aoe burst and a dash. mf does more sustained damage

the dash is more than you think