So I'd been to the A's colleseum for years as a child to enjoy baseball games with my family. I've been to Candlestick when it was the home of the Giants. Both seemed huge, and dirty. The new Giant's stadium is AMAZING. It is significantly smaller than the other arenas, and the view from each seat seems closer to the field, even when high up in the upper sections.
The best experience I've had at a baseball game EVER was when I went to the Giant's stadium and sat on the Club level. For not much more money, it is a very uncrowded way to go. I'm not a big fan of large crowds or being pushed, so the Club level was great for me. The bathrooms were perfectly clean, I was so relieved to find. The food options are extensive, from caramel apples to garlic fries to sushi to smoothies. If you're going to a game, go to the Giant's stadium. It's a wonderful experience.