ICS are good out of the box, the only issue with them is their external compatibility
G&P I consider still an upgrade platform gun. They never did fix the issue with the gears and the pistons are still hit and miss. So you could have a G&P last 3 years of very hard use, or it could break a gear axle the first game you use it. And their aptly named "explosive" piston heads are almost guaranteed to break after a year of use due to their weak design.
You don't buy a G&P for internals, you buy it for externals and then upgrade the shit out of it.
Even then, VFC is proving to be the all around better platform. Similar build quality and durability, with much better stock internals.
But G&P still has the best designed M249 on the market by far.