I was kicking around the same question recently. My choices were the ACOG 3.5x35 with the BAC, the Aimpoint Comp ML, and the Shepherd Scope. My main concern was quick target aquisition, with range finding(RF) and bullet drop compensation(BDC) as a bonus. I ended up getting the ACOG for a couple of reasons. The Aimpoint Comp ML although much cheaper needs batteries. As a "survival" optic, batteries might be few and far between. Also, there is no RF or BDC built in.(also electronics can and do break).
The Shepherd has a reputation of being extremely robust, accurate, and has the RF and BDC built in. The problem with the Shepherd IMHO is that like most scopes, it does not allow for rapid target aquisition. But if you want to "reach out and touch someone" at GREAT DISTANCES, this would be my choice.
I ended up getting the ACOG TA11 for many reasons: it fits the AR handle perfectly. It has a channel through it's bottom so you can still use the iron sights if necessary. It has the RF and BDC (out to 800 yards), a bright red "donut" display that adjusts to the ambient light(the donut is brilliant in any sun light), as well as tritium for use in low light conditions. It also allows you to use 2 eye open sighting which gives you a better view of what's going on "out there". It's also shock proof waterproof, etc. The MSRP is around $1300 US, but i've seen them for as low as $800. Botach
http://www.botach.com/ has them on sale for this price right now. Hope this info helps!!!
Andy