Rob from TacticalYellowVisor.net has a few great comparison charts that he was kind enough to make public.
These charts cover all major brands, and should make it a lot easier to narrow down your next purchase based on your wants and needs.
- Comparison Chart of Major Brands of M4-Pattern Carbines
- Comparison Chart of Aimpoint Models
- Comparison Chart of Various Free-Float Rail Systems for AR-Pattern Carbines & Rifles
- Comparison Chart of Major Brands of 5.56 Sound Suppressors
Although these charts seem to be updated from time to time, they may not be right up to the current date. They are meant as a guide, so do your own due diligence when finally deciding what to purchase.