Well, I thought 00 was the best of the series. It felt like the Gundams were the most advanced within the Gundam Century Timelines. With their slick designs they didn't need the huge backpacks to be able to fly in or out of the atmosphere. Just throw a GN Drive in a huge mecha and you're good to go

*I said "it felt" because the most "advanced" Gundam is shown in Turn A .. I won't say who's that so I don't spoil anything
I think that the difference you brought up between the Gundams and the other MSs can be explained by remembering that, in other series like the first one or Zeta, there were always technology "exchanging" between rival parts. Like when the Mk II was stolen and right afterwards Zeta gets designed by Kamille, based on the MS made by his father. Seed and Destiny also show technology being robed in their first episodes. With them, the coordinators were able to produce new MS based on the earth's concepts, which led to the look-alike-mobiru-sutsus
Something like that only occurs further into 00's first season, with the false GN Drives powering the mass producted GN-Xs and later adaptated into the Enacts. The Gundams were produced completely independant from other mechas, looking really different.
The soundtrack of both seasons is also simply the best in Gundam's shows and among many other animes as well. Not to mention Miss Sumeragi Lee Noriega
So this is my
Char[t] (loved this!)
1. 00
2. Turn A
3. Seed
4. 8th MS team
5. MS igLoo
I've also heard a lot of good stuff about Wing including it's similarities with 00. Like the concept of gundams bringing peace through war. Can't wait to watch this too!