Mahle is one of the biggest automotive manufacturers in the world, providing OE pistons for countless engines. It's not surprising that their motorsports division are renowned for producing some of the best forged pistons on the market, they come highly recommended here at H-Tune.
4032 Alloy Pistons:
Mahle's high silicon content 4032 aluminum alloy and their forging process allows for a strong, lightweight piston and a very low thermal expansion rate. This means that the piston will expand along the lines of your factory pistons, giving you improved performance while retaining the factory reliability like a cast piston. This also means there's little risk of piston slap on a cold start, characteristic of many forged pistons. Data sheet provided with cylinder wall clearance guidelines. It doesn't get much better than that when it comes to forged piston technology.
For many daily-driven builds, 4032 pistons are the best choice you can make for longevity and cold start driveability. Very popular for Honda K-Series and Subaru EJ engines in particular.
2618 Alloy Pistons & Gold Series:
Some heavy-duty big-horsepower applications are made with 2618 aluminum alloy and also feature hard anodised top ring land as noted in the options above. This alloy has a lower silica content and higher expansion rate, making it more akin to a traditional forged piston. Those with huge turbos or dedicated track slags are best looking here.
For vehicles with a FRM cylinder lining (Fiber Reinforced Matrix), such as the F20C/F22C (S2000) and H22A (Prelude/Accord Type-R), Mahle has a special series called the "Gold Series". The Mahle Gold Series pistons have a special skirt coating that allows the piston to be dropped into the FRM cylinder bore without needing to sleeve the block. This sacrificial coating is a completely unique feature to Mahle pistons and one of the reasons they're likely the only piston you'll hear recommended for these engines.
All Mahle Motorsports Forged Racing Pistons are sold in a complete set of 4 pistons and come complete with wrist pins, piston rings and pin locks.
On a few engine fitments, such as Honda B/K-Series and Ford Duratec you'll notice that compression ratios are given in ranges. This is due to various engines in the series producing different compression ratios based on numerous factors (deck height, stroke, head gasket thickness etc.) For example with Honda K-Series, the lower value is for K20A/K20Z applications, and the higher value K24A.