I bought a Razer Deathadder a few days back, mouse is absolutely perfect, beautiful design, comfortable as hell(more comfortable than Logitech G500), smooth feet glides over mousepad and I hate it.
Why you ask, because, lets start shall we, it needs to connect to internet to work, you can't even install it offline(eg: if you downloaded it elsewhere), it won't work as it downloads some additional software at install time plus first time you use it you need to connect to internet as it creates and syncs profiles, this step can't be skipped.
Next, well now that's passed, you think it will work, oh no, after restarting pc everytime it attempts to connect to internet, during this time the mouse is basically useless as DPI is pushed to max(3500) and also acceleration is maxed as well, try using that, after some time it will time out and works normally, but that's 3-5 mins lost. And also during sync the mouse sometimes halts and jerks.
Now another issue, time to time the profile in cloud would get erased or corrupt and generate a mismatch with local profile, pray dear lord, what the f**k is the use of cloud then? Another problem as the entire profile that you had worked on for minutes is lost.
Another big issue, when profile switching, mouse halts and skips making a mess.
Final big issue, every profile can be associated with one and only one program, so for say a dozen games I need a dozen profiles, have I told you I hate razer?
All these issues were nonexistent in case of logitech, offline install and use, profiles were locally created and stored, now razer fans may argue about cloud blah blah, but and I did something ingenious, linked the local profile storage directory in my documents to google drive, problem solved, I could download the profiles to PC( a few kb), or simply sync using google drive, also logitech software could switch profiles seamlessly without interruption and infinite no. of apps could be linked to a profile(I had 4 profiles only, Desktop, Shooter, HacknSlash and Browsers).
Logitech wins, period.