I'm new to AR-15's, but I'll throw my $.02 worth into the pot, for what it's worth.
I went with absolute co-witness. I have a ARMS 40L (SP) BUIS behind my 552, and a Troy Fold down Front site in front. Both can be easily flipped up if needed, but are out of the way otherwise.
I asked similar questions when I was building mine. I got a lot of help from the "big bad BUIS thread", and from the other good folks here. I was concerned about the front A tower interfering with my "field of vision". Some said you won't notice, other said it bothered them. Everyone agreed I should try it with the A tower installed and decide. Which is what I did. It bothered me, so went with the Troy front site.
I like this set up because once the rifle is sighted in, then everything lines up, and the Iron Sights are there if I want them. Out of the way otherwise.