Hi again 1exotic.
Don't worry about the questions, it's fun to help
I had 2 lenses kit on my film SLR and bought the Tamron 18-200 with my 350D becuase I didn't want to change lenses all the time.
The 18-200 is nice but have some problems (mainly focusing speed, resolution and focusing on low light). The 18-250 should be much better than mine.
The main questions are: what is most important to you? And what is your budget?
If you're looking for 1 versatile lens, maybe the Sigma or the Tamron is your solution, I don't know much about the Sigma but you can read a good review here: http://www.photozone.de/8Reviews/lenses/sigma_18200_3563os/index.htm
and about the Tamron here: http://www.photozone.de/8Reviews/lenses/tamron_18250_3563_canon/index.htm
I decided that the resolution and fast focusing is most important to me so I'm splitting my range into 2 lenses again: Canon EF-S 17-55 USM IS (hope to buy it this or next week) and later probably the Canon EF 70-200L f/4 USM (with or without IS).
Of course, these lenses are excellent but also quite expensive.