Only you can define what better means to you.

The EF 28-105mm f/3.5-4.5 II USM was introduced in 2000. I'm assuming the older lens you are using is the EF 28-105 f/3.5-4.5 USM (the previous version) introduced in 1992, for which I could find less test data. As far as I can ascertain, the two versions of the lens were optically identical and the changes to the "II" were only cosmetic. There is also a much smaller and lower quality EF 28-105mm f/4-5.6 introduced in 2002.

The EF 28-135 f/3.5-5.6 IS USM was introduced in 1998. It was the first standard SLR zoom to use Image Stabilization.

Both of these lenses were designed in the 1990s for use with 35mm film cameras. There isn't a lot of difference between them optically. At 28mm and wide apertures the 28-135 is clearly sharper in the center, but the 28-105 is just as sharp by f/5.6 in the center. The 28-135 is generally sharper at the edges across the entire range, but not by a lot. As we would expect, the higher zoom ratio of the 28-135 leads to a little more distortion at the wide end, but both lenses are pretty good in this regard. The 28-135 also demonstrates a little more vignetting than the 28-105. At most common focal lengths and apertures both lenses control CA fairly well for their price range. The 28-105 has noticeably more at 28mm when using narrow apertures above f/8, but has slightly less CA than the 28-135 at most other focal lengths and aperture combinations. Although they both start out with maximum aperture at 28mm of f/3.5, at 35mm the 28-105 is f/4 while the 28-135 is still f/3.5, by 50mm the 28-105 is about 1/3-2/3 stops faster than the 28-135 through 105mm.

What it really seems to come down to is:

• The 28-105 is 6 oz. lighter (13 oz. vs. 19 oz.), but has less reach and no IS.
• The 28-135 is larger and 50% heavier, but slightly better optically, has 30% more reach on the long end and first generation IS that is good for about two extra stops when shooting static scenes handheld.

When factoring in the weight of your 7D body, the 28-135+7D is only about 13% heavier than the 28-105+7D. In return you get more reach, slightly better optics, and some IS.

Links

http://www.photozone.de/canon-eos/189-canon-ef-28-105mm-f35-45-usm-test-report--review
http://www.photozone.de/canon-eos/190-canon-ef-28-135mm-f35-56-usm-is-test-report--review
http://www.the-digital-picture.com/Reviews/Canon-EF-28-135mm-f-3.5-5.6-IS-USM-Lens-Review.aspx
http://www.the-digital-picture.com/Reviews/Canon-EF-28-105mm-f-3.5-4.5-II-USM-Lens-Review.aspx
Comparison ISO 12233 charts between the 28-105 II and the 28-135