Which one is better - colectomy or remicade (infliximab) for left sided colitis? Advice from 2 different gis.

Hard to say. It all depends. Surgery is usually reserved for medically refractory toxic disease or dysplasia/surgery. Most patients with severe disease will have an opportunity to respond to medications such as Remicade (infliximab) or cyclosporin before surgery is performed. Colectomy is curative but having an ipaa also presents problems.
Case by case basis. The particulars o your case typically will guide you and your doctor as far a the best available option for you.