XFX - Pro: Double lifetime warranty if you ever want to sell it. Also they are a pretty decent company overall.
- Con: No voltage tweaking to my knowledge so overclocking overall, then again 6870 doesn't OC much. They don't have custom 6870 coolers so they'll run hot-ish.

Sapphire - Pro: Good well respected company, custom coolers. Trixx or something like that for Sapphire card OCing, and also pretty decent overall company.
Con - Meh when it comes to support. They're alright, not as good as XFX to my knowledge.

si no le entendiste ve por la xfx jeje saludos.

Te recomiendo la Sapphire, trae muy buen cooler y como te comentan arriba puedes instalar la aplicación del fabricante "Trixx" para hacer un overclock (si te hace falta).