What are you trying to accomplish with your downspout filter? Do you want something that blends in and looks great? That would be the SlimLine.
Looking for less maintenance? Then the open faced would be a better choice.
Want to place the downspout filter unit right on top of the rain barrel? Barrel Topper or Guardian are the ones to review.
The First Flush products capture the beginning of the rain event and then allow the cleaner water to go on over to the tank.