You really can't go wrong with either system, but if you want, "everything fitting and not having to plumb anything" then you may want to consider that the Waterbox will have US Standard plumbing while the Red Sea will have Metric plumbing. You will either need to make sure the return pump you purchase has the same size barb fitting or get a little creative with adapters that may or may not be easy to get at your local hardware store, (depending on where you live). It will also be a consideration for any future modifications once you get comfortable enough and ever decide to upgrade or add additional equipment that needs to be plumbed into the system.
That being said, it is pretty easy to get adapters online to fit any size plumbing and there are lots of people on here that can help. Just thought I would point it out since you brought it up.
As far as the cabinet for the Red Sea goes, I am curious what you have heard that is bad? I have had no issues at all with it and from my experience so far, I really like it. I cannot think of anything that I would consider bad about it.