If this is going to be your first kit, keep the quality of the instructions in mind. With your RTF trainer and the ARF glider, you probably got a fairly complete set of instructions that took you through the assembly process. Depending on the kit, you can get anything from a set of "step-by-step instructions" to a very bare-bones "contruction guide", which says "... build the fuselage, build the wing, and put 'em together" without a lot of details.

Your other problem is that there aren't a huge number of commercially available kits for twins: NE-Aero and Cedar Hobbies have some sport models; Hobby Hangar has the Uravich 53" OV-10 Bronco (good kit, but not one I'd recommend for a first kit build). Tower used to have a Great Planes Profile P38 Lightning (Complete instructions, but Lightning's aren't reco'd as first twins). Wing Manufacturing has a short kit for an A26 and a P82 Twin Mustang. Your Twin Otter is an attractive airplane; if the supplier's instructions live up to their billing in the ad it might be a good choice. And if the time/money equation plays any part in the decision, the $120 TwinStar ARF merits consideration: it's not a kit, but you'd probably end up getting it in the air sooner.