Yes, a fast pokemon is useful. I'd suggest tanks to endure those annoying random attacks, such as Metagross, Milotic and Latias, and then someone that is useful to attack and rid the team of status problems. Altaria might be OK here.
Beware of Brandon's Registeel. Regice was easy to beat with my Metagross, but Regirock used explosion on my Latios. However, Registeel uses Toxic, then Iron Defense all the time. It also has Leftovers on it. For steel types and others, it then uses Earthquake. My team was Latios, Metagross, and Latias. It wasn't the best team, but I still won. Barely.