Depends on cam specs you will be running as to the ratio.... We used to run a bigger ratio on the exhaust valves, trying to scange a bit... No idea if it ever helped or not.... Now about all I run is stock ratio, guess I prefer the good ones from Comp Cams, they're moly.... a bit more expensive but we're racing with them. For the average street usage type engine most guys just run the aluminums. Lots of folks are running the Harland Sharp aluminum rockers and even some of the import rockers and seem to do just fine with them!!!
A consideration, if a rocker breaks, then a lifter can pop out of the lifter bore and there goes your oil pressure...... guess I wouldn't be real confident just settling for the cheapest rocker arms!!!!!