>>2008210There are a few things to consider when buying a rack.
Firstly, 'disc' racks.
The middle and right rack are 'disc' racks, meaning that they have a recessed bolt hole to work around a disc brake.
This means that the bolt is obscured, you can't tighten it with a multi tool, and if the head strips, it's more difficult to remove.
It's worth avoiding disc racks unless you actually need one. Looking at your pic it seems like a standard straight arm rack, like on the left, would work fine on your bike, because your disc brake is not really in the way.
Secondly, adjustable lower arms
The rack on the right has lower arms that can be adjusted up and down. This adds a point of flex and failure, and is also worth avoiding.
So then you'd want to chose a rack which is high enough to clear your mudguard. It's easy to measure that. Most 700c or 650 racks will do it.
It's nice to have a rack which is not too wide, or too high, although if they are extremely close you have to take more care loading them to not get stuff caught in the wheel.
Thirdly, dual rails
The rack on the left and the right have dual top rails. This means you can run panniers lower, and the panniers don't mar the racktop. This is a big advantage and a design of decent touring racks.
As for the upper struts, don't worry about it. You can attach them with p-clamps to your frame, or directly to your seatpost clamp. They can be bent. It's not a compatibility issue.
Width of the rack arms is also not an issue. You can just bend the rack to fit (actually bend it though, don't have the bolts bending it closed in tension).
As for getting a tighter cassette because your shifting skips and is rough, that is bizarre. You bought a stock bike right? The gearing should fucking work. You shouldn't have to modify it to make it work. I don't see why that mech can't shift a 40t cog. Sure winding your b spring in a bit will improve shifting but it shouldn't go from 'actual problems' to 'works correctly'.
