Well the difference is obvious to me. The sensation is on HSDPA and the other is on EDGE... Two different LAC and CID codes as well, which is the cell tower identifier.
Your first problem is that you are on two different towers. The second (and more relevant problem) is that you are on two completely different networks (HSDPA vs EDGE), and it is normal for the signal to be very different between them. At my workplace I get full EDGE signal but only 1 to 2 bars of HSDPA.
Force the Sensation onto EDGE and I bet your signal will go up.
I still prefer HSDPA even with 2 bars, because I can get high speeds and perfectly fine calls with even only one bar, while EDGE is basically only good for voice these days, no matter the signal strength.
To illustrate the awesomeness of the Sensation and HSDPA, I was in Tijuana last week about 10 miles from the border and got 2 bars (full signal if I was on the roof) through T-Mobile. 1 to 2 bars was enough to serve wifi to 4 people easily. I was getting 75KB/s both ways with 2 bars... nobody else on T-Mobile was able to use their phones... and only occasionally on the roof.
The only gotcha is that the Sensation does not like having its back covered, and for some reason performs more consistently in landscape mode. When on a table, it wanted to be face down.
And the weirdest part... when face down, the speed would increase by 15 percent or so if I lightly placed my pointer finger about 2/3 of the way down the phone in just the right spot. Human antenna I guess.
Yes, the Sensation suffers from some grip issues, but it is far outweighed by being able to serve up high speed internet and make calls when nobody else can when you know where not to touch it.
Lastly, I worked in T-Mobile's corporate engineering department in Bellevue for several years testing new markets, new technologies, and major changes to network architecture... used a LOT of different phones and there is no perfect phone. They all have an Achilles heel. It just depends on what you use the phone for.
