I find when i play watch dogs there the mouse i have is a little twitchy and all over the place, but when i play titenfall it slow.
Yup.
I have games where the mouse is really twichy in-game, but slows right down even in that same game's menu!
Easy solution - Find the DPI you're happiest with for general usage, ie in Windows, Office, File Manager and whatever else you use your PC for. Then add a number of settings either side of that and assign one mouse button to cycle through them.
I run 1080p on an OCUK XXL mat and both my mice are set to about 2500DPI. I can go up two increments to around 3000 or down to around 1600. This is a pretty low setting, though.
However, I 'claw' my mouse, as in my wrist never moves from that spot and I move the mouse with fingers alone. This means small movement on the mouse translates to pretty large movement on-screen, which usually requires a fairly high DPI.
If you like to make lots of wide movements across the mat, you'll usually have a lower DPI.
Both my CM Storm Inferno and my Logitech G700S can each go up to something like 8500DPI!!
Basically, play around until you find something you're comfortable with. As mentioned, the more important aspects centre around what feels most comfortable for you (try some out in your 'local PC shop', if you can) and what features best fit your requirements.
Most gaming peripherals are about enhancing and tailoring your personal experience, rather than offering any notable in-game advantages. Some people are happy with just a very basic mouse.