It is hard to say since both sets are close. RotV is more of a general set which is great for people starting out especially while SotM is more of a themed set for people who own the first. I actually got SotM at a sale first and liked it enough to buy RotV at full price so in my opinion both are great on their own
I would have to give the edge to RotV since it does have more terrain (although the swamp water is nice) and it does have a few more figures.
As for having the duplicate characters... initially I was dissapointed but after going over the cards I realized that you were still given options. Since quite a few people use Raelin and Drake chances are that they will be drafted. But which one do you prefer? You might play a scenario where you have to defend a castle but only have half the points of the attacking army. You may want to go with the cheaper Raelin who gives a stronger bonus but at shorter range (since you may want to pile the walls with squads). Then again you may be the attacker with more points to spend so you choose the more expensive Raelin. Although her bonus is slightly weaker it's range is longer thus allowing your army to span ahead of her a bit easier... also she is a bit more durable in combat and her whirlwind attack may be usefull in taking out some squads up on the walls. The new Drake is better but more costly... you decide which one would be better suited to your situation.
Also getting 2 doubles when you get over 50 characters is not such a huge deal. But with all that being said I would not like to see it happen often if at all. I think original characters are the way to go although I can see how fan favourites may come back with a slightly different costume and a new trick up their sleeve... but it should be rare if ever again.