Oi, all this again....
All factory pistons are cast.
Aftermarket cast pistons come in two varieties; OEM spec and slight redesigns like the Mahle race cast. Besides the steel ring land, the cast are more dimensionally stable. So they don't require the PTW clearance to accommodate piston growth. You want this for daily driving. If you make sure you have abundant piston cooling and your oil pump doesn't cavitate you should be good for lot of race passes too.
Forged are stronger, but lack the integrated oil gallery. They grow a great deal with load. They can be used in a daily driver, but there are a number of builder decisions and compromises that will have to be made. That would be a whole 'nother thread. In short, you pick where you want the engine to perform, and sacrifice outside that application.
The oil gallery is very important for long term reliability over a large range of loading. Yea, it keeps the piston as a whole cooler, but it is paramount to keeping the ring package cool. Without it, like in forged, you have to gap your rings for the worst case. With the gallery, you can keep the ring gaps a lot tighter and thus limit blow-by.
