Airsoft Red Dot or ACOG?
Red Dot: $20-$100+ Generally good for CQB (0-40 yards) and anything that requires quick target acquisition such as building clearing and dense woods. Good all around sight in my opinion. Can be used effectively out to 100 yards with practice. ACOG: $700-$1300 Even the off brands are expensive, these are wicked good scopes and give a nice advantage. Can be used from 0-200 yards (I haven't done much airsoft but I know they don't shoot far so I'll just say 200 yards), and with a lot more practice can be used in CQB albeit the Red Dot or Reflex will be better choices as they block less of your field of vision and have no zoom. Personally for even if your playing in wide open areas I would go with a Red Dot, the price is incredible for ACOG's and since you're using an Airsoft and not a real gun you be wasting all that potential. Red Dot is an all around scope choice and the ACOG excels at everything except CQB which can be offset with practice and drills.
Aimpoint or Eotech which do you prefer ?
Eotech, it holds a zero much better than those aimpoints
M4 airsoft red dot sight won't work HELP PLEASE?
The red dot sight shouldn't be part of the gun, first of all. Here are possible problems: 1) You got a bad sight (probably not the case) 2) Something's wrong with the battery housing (happened on my EOTech holographic sight) 3) Out of battery 4) Other internal problem (loose wire, loose screw, etc.)
Will a red dot sight withstand an airsoft BB?
Your red dot sight should be just fine. Those are pretty durable and I highly doubt an Airsoft BB would do anything but bounce off.