Broadband Tweaks → Advertised vs. Real life speeds.

I use Comcast cable as my ISP in Mount Prospect, Illinois.
While speed tests with some servers confirm the advertised speeds, majority of speeds are lower.
Real life download speeds are MUCH lower.
Would it make sense to try switch to AT&T DSL, which is offering lower speeds, but is charging much less?
I would like to find out whether AT&T is offering more honest advertising speeds/real life speeds ratio.
Current Comcast discrepancies between advertised and real life speeds are simply too big.
Share your thoughts, please.

Speed will vary by server, location, the load to/from/on that server. My speeds aren't very ideal to all servers/websites either, they aren't all created equal.

Also if you have other people using the connection it depends on their usage too.