Which one do you like better and why. I currently have the standard ones on my carbine but am wondering if there is a good reason to go to the M4 ones. Never used them before.

I prefer the M4 handguards simply because the regular CAR handguards are so narrow.  The M4 handguards are also made of a better quality material than the Bushmaster CAR handguards I tried and the double heatshields make them more comfortable to hold onto.  But it is the more comfortable feel that I go for.

The prime reason to switch from standard carbine handguards to M4 style is heat. If you aren't having problems with heat build-up, the only thing you'll gain is different ergonomics (some like it better, some don't) and a fatter handguard that may interfere with slings, extended receiver mounts, forward carry handle mounts and other things designed with the standard carbine handguard diameter in mind.

i switched to the M4 style on mine is not just for the heat, although it help in TX heat, I like the feel of them better, more "meat" to hold.

I have smaller hands, and don't really like the girth of the M4 handguards.  If I was having a heat problem, I'd consider them.  But, my pitiful semi-auto doesn't seem to generate the heat.  

If you plan of throwing any type of rail on your hand guards, don't use the M4's.  You'll end uo detroying the heat shields.  I like the regular handguards.  More accesories out there  that won't fit over the M4 guards.  The Cold M4 handguards are made with a nicer polymer than my Bushy's.  I'll admit to that.  Usually I use the Mag well as my fore grip so heat wasn't an issue.  Also all the gear I have won't fit on/over the Colt guards.  They're actually just sitting here on my desk.