GDI still use M113 "gavin" tracked armored personel carrier in the timeline of Renegade. It still produced in the War Factory. Its armor is reasonably well, suggesting an upgrade have taken place, as its armor and machinery can shrug off several heavy attack (including a direct hit from Nod's Obelisk of Light) before the vehicle become incapacited. As the name imply, it can carry multiple personel at a time, with driver control the vehicle and mounted machine gun.
After the war, GDI started using Amphibious APCs to quickly move infantry over bodies of water instead of just land, trading its machine gun toting and some of its armor with amphibious capability.
The entire vehicle needs to turn to train the gun and can fire on the move, albeit with limited degree of aiming. The vehicle is quite mobile although not as fast as Humvees or Buggy. The APC can squish infantries and have secured live support module to protect against Tiberium hazzard when navigating inside Tiberium field..
In Tiberian Dawn Nod does not use the APC with the exception of some campaign missions where Nod uses stolen M113 APCs. However Nod use modified four-wheeled BRDM as their APC in the time of Renegade, with no major difference with GDI.