Best gundam show is Gundam Seed (for character development and theme) and then Gundam 00 (for combat and action). Both of these shows have the better sound tracks than any other gundam shows.
IMO it is a lot better than UC stuffs and even the most recent ones. Gundam Seed is a much improved remake of the original gundam with more emotional story, character developments and bond. They had more than 20 years to improve it. You have to ignore the recycled footage thou since it's the first gundam that is not hand draw and a lot of the budget go into sound tracks. The mech design is still beautiful and aged well thou. It's a drama show first, mecha second so if you just care for action sequences or strategy it may not be the best for you. Yes it has giant robots, but its main character is a young boy being thrown in the middle of a war unprepared. It is revealed at the end that the boy is not just a normal person (or even a normal coordinator thou). It's not transformers, and the series pick up gradually and become amazing later on. The sound tracks also help create a lot of emotional impact.
The ending of Gundam Seed last episode with Find the way is still one of the best anime ending I have ever seen.