Which has better glass and better internals? Any other notable differences? I'm confused by the Nikon lineup these days.

The PS5 is basically an upgraded Buckmaster. The Buckmaster II is a new line which is their bottom of the barrel line. I would stay away from the Buckmaster II but the PS5 is a decent scope.

Nikon's PROSTAFF 5 is a higher quality riflescope then the Buckmaster II. The PROSTAFF 5 offer's better glass coating's for and parallax adjustment. Both are backed by Nikon's outstanding No Fault Policy.
I have used the PROSTAFF 5 and found it to have a crisp clear view down the tube and the BDC reticle combined with Spot On provides excellent longrange accuracy.

http://i1216.photobucket.com/albums/dd363/bman940/PROSTAFF%205/prostaff5416.jpg

Bart, this may be a dumb question, but why did the prostaff start out being their bottom of the barrel scope and now it is better than the buckmasters series????? Thanks buddy..

The ProStaff was their bottom line and the next step up was the Buckmaster. They got rid of the Buckmaster and replaced it with the ProStaff 5 (and upgraded it) but they must have wanted to continue to use the Buckmaster name so they brought out the Buckmaster II which is lower than the ProStaff. I'm guessing a lot of people who don't know better will think the BM II is still the old BM and buy it on the BM's reputation.

They also came out with the ProStaff 7 and Monarch 5 this year. This is to complete their 3, 5, 7 lines.

Reelman is Spot On....
Since I only do freelance work for Nikon I'm not involved in those decision's.
I know part of the 3-5-7 desigantion is to make it easier on the buyer. The Buckmaster line has been a big success for many years so it was really never phased out and now with the Buckmaster II it is alive and well. I haven't had my hands on one or a PROSTAFF II so I can't really comment on them other then what Ihave read and been told. The PROSTAFF 5 and 7 are defintely not your PROSTAFF line from years gone by. Some friends just got back from a shoot where they were hitting targets at 1200 yards with the PROSTAFF 7 BDC reticle.
I have used the MONARCH 3 and it is very nice. Extremely clear,bright and great for early morning or late evening shots. The 4-16 BDC made pinging steel at 500 yards pretty easy.

http://i1216.photobucket.com/albums/dd363/bman940/MONARCH%203/MONARCH34-16.jpg