I bought the Canon for my fiancée recently, and its image quality is good for a 18-200. I do wish it had the ultrasonic motor. What I know 'for sure' are:
1. It's not 'twice as good' as any lens that cost half. Since you can't quantify such things;
2. The resale value is much better with the Canon. But since you're buying either used or refurbed, you won't lose much either way.