Just use both and avoid the dilema. Most people will say the the front grip and the other half will tell you the laser. Others like the front w/ a supp for silence. Really it just comes down to a matter of preference. Try them out for yourself and find a combo you like. For example, you can have an IW or STG with both equipped, and they work just fine.
Yeah, its a cool concept, but I think they are over-hyped a bit. People do just fine with other weapons that don't use these attachments. All a matter of personal opinion.
With a silencer, without question rifle laser. Considering it gives you a nice big red dot which makes it so much easier to focus on shooting the enemy.