MrPbody is on the money
We've seen cases where just switching rocker arm ratio has created pushrod clearance problems with the head, so you should check.
Ratio changes are usually applied to either the exhaust and/or intake side to compensate or test for inefficiencies in head port or manifold flow -- that said, it may be a better idea to just get a cam with more lift and/or different intake/exhaust numbers (lift, duration).
The roller, on the tip and/or the fulcrum reduces friction in the valvetrain primarily, and secondarily, "good" aftermarket rockers in general are more accurately machined than the stock stamped factory rockers.
Aluminum vs steel is another choice -- aluminum is lighter, but more expensive and less durable than steel (I've seen both broken though).