Bad ram causes instability and other problems. Give you an example. A bud didn't know what he was doing and got PC3200 Ultra brand ram with Elixir chips. Well, it was very unstable, so he let me try it. I could barely get it above 170. Past that, regardless of voltage, timings, etc, the system became very unstable. I even had my pc boot off it wiht a corrupt windows file.
Moral: stick to good ram.
Now, you're considering different brands of good ram. OCZ, Kingston, Buffalo etc. OCZ tends to be expensive since it oc's far and does good timings. If you're ocing, it may be worth it. Buffalo is a cheap brand ram that uses/used awesome Winbond chips. They gave really good performance for very reasonable money. Kingston Valueram is perfectly fine at default settings, though it may or may not run good timings and overclock far. Personally, I've been lucky with both valueram sticks I've worked with: they could both run one speed grade higher than advertised (2100-->2700; 2700-->3200). It's up to you.