I think I've narrowed it down to 2:
Roccat Savu or Zowie FK.
Both have their pros and cons. The Zowie website is terrible... it's really hard to find out info about their products!
TLDR: zowie fk or logitech g400/g400s.
(i have also read great things about the razer deathadder 2013 and steelseries kana v2.)
..i vouch for the zowie fk. i own one.
i also own a logitech g400, another mouse i vouch for.
both mice use the best optical sensor and have no acceleration.
both mice do not need drivers (although they are available for the g400).
both mice have buttons to change the dpi on-the-fly with.
which one you'd like more just depends on your preference of shape/size, weight/weightdistrubution, materials, switches and scroller.
unfortunately you're have to guess which one that would be.
the switches used in the g400 tend to be more universally liked, but the g400 has a relatively weak cable. the g400s is supposed to have a less weaker cable than the g400.
extra info:
Zowie FK:
Zowie FK (true) DPI steps: 450 = 477, 1150 = 1188, 2300 = 2386
Zowie FK native DPI step: 2300(2386)
Zowie FK default polling rate: 1000hz
Zowie FK uses Huano switches.
Zowie FK has a slightly lower lift-off-distance (thus the weird 'true DPI steps').
you can change the polling rate on the zowie FK on-the-fly by (unplugging it and then) plugging it in while holding a specific button (combination).
- hold front (left) side button: 1000hz
- hold back (left) side button: 500hz
- hold back (left) and front (left) side button: 125hz
G400:
G400 DPI steps: 400, 800, 1800, 3600
G400 native DPI steps: 800 and 3600
G400 default polling rate: 1000hz
G400 uses Omron switches.
there's a newer version of the g400; the g400s. i presume the g400s is just as good as the g400 but i haven't looked up the specifics on it. i think the only real change is the last DPI setting is 3600 on the g400 and 4000 on the g400s.
bonus info on the g400:
angle snapping(prediction) on the g400 snapping was removed as of PID LZ13333.
any g400 that has a full serial number and not a PID has angle snapping disabled.
any g400s has angle snapping disabled.
edit: i probably have already given alot more info than you wanted, but feel free to ask me if there's anything else you'd like to know about either of these mice :j