I have a Hero and an Evo and my wife has a Hero. Between the 2 of us there are 5 batteries. 1 stock Evo 1500mAh, 2 stock Hero 1500mAh(1 of which is actually from a TP2), 1 Seidio 1750mAh, and 1 Andidia 2000mAh. I have tested all 5 batteries in both my Hero and my Evo, and I will slip the wife a different battery now and again without her prior knowledge and see if I get and 'feedback' about piss poor battery life.
Now this is where things get strange, the Evo and Hero batteries are very similar and rather interchangeable, that is where their similarities end, Aside from being different colors, the Evo battery outperforms both Hero batteries in whatever handset I put it in. Now I suppose this could be completely coincidental since The test variables were different each time, however, all tests(except the wifes) were performed while at work, where I have fantastic service, as there is a cell site mounted to the building. The day to day usage differed slightly, but I don't believe it would be enough to skew the results that much.
All of the HTC batteries outperformed the Seidio and Andidia batteries.
In closing, I would recommend the Evo battery. A few other handy items are an external charger for your extra battery, and a business card holder. Why a business card holder?, it gives you something to keep your spare battery in so it doesn't short out against change or keys in your pocket, and it adds some protection for the battery, you wouldn't want something to pierce the wall of the cell(s).