I have owned both a Sun Mountain Speed Cart V2 and a Clicgear 3.
They are both excellent carts. You would be happy with either one.
Differentiators:
Sun Mountain is easier to fold and unfold. The price you pay for this is that it is larger when folded. If you have small car with a small trunk, this might be important. If you have a large vehicle (SUV, for instance) the difference is unimportant.
The Sun Mountain holds the bag at a more reclined angle than the Clicgear. It does this because it doesn't employ straps to hold the bag on the cart. It uses adjustable arms that cradle the bag and that rely on gravity to keep it in place. As a result, the clubs are hanging at a slighly less inclined angle to the ground (closer to horizontal) than on the Clicgear, making it very slightly harder to get at them. Not a big deal, but something that bothered me a bit.
Neither use pneumatic tires, but the Sun Mountain tire is an otherwise standard looking tire - relatively narrow. I believe that it is made of foam. The Clicgear tire is a broad (perhaps 2" wide) surface covered with a thin layer of rubber. I would imagine that the Clicgear has a larger surface area on the ground, which would tend to produce less weight per area in contact with the ground. Difference would not be great, however. I didn't find much difference between them when traversing boggy areas.
The Sun Mountain had a nice sling for putting a sweater or other item under the handle the the Clicgear doesn't have (because of the way it folds up.)
Beyond that, its a draw. Both have enough storage for whatever you might want to take. Both have a decent brake. Both steer true. The Clicgear has a few more options than the Sun Mountain (things to hang off the cart, like a container for your laser, an insulated drink holder, etc. The Sun Mountain has an option for a footstool attached to a leg if you want to sit (I have no idea if this works well or not.)
Both have nice umbrella holders that attach to the handle for rainy days and they work quite well.
I ended up giving my Sun Mountain to a friend and am using the Clicgear, mostly because of the "angle of the dangle" mentioned above, but every time I unfold and fold up the Clicgear I am muttering to myself about how nice the Sun Mountain was.
Hope this helps.