I'm far from an expert, but I personally see no point in anything but a flat-top upper, no carry handle of any sort (tactical, standard or optic-specific), unless one is going for a retro look or one intends to shoot only with iron sights. A pure flat-top enables you to add a BUIS and whatever optic you want. And if you later decide that you must have a Dominator or some sort of tactical handle, you can add it.
If you are using this as a general rifle and have no optic, at present, to add to it, I'd either:
1. Get the A3 carry handle. It's pretty cheap, and gives you iron sights.
2. Get flip-up irons and no carry handle. This might cost a little more in the short term, but in the long run you won't be buying an A3 handle, then an optic, then flip up irons. The downside is that the rifle looks a little odd with flip-up sights and no optic, but pretty is as pretty does.
EDIT: On send thought, depending on the BUIS, it might not cost more. It could even be cheaper.
I would not worry about a dismounting or flip up front sight post. When using a red dot or optic I never even notice the post, and it is one more expense and one more thing to go wrong.
JMO,
Mike