Floors, tiles, doors, sanitary installations, windows, heating, electrical, stairs, gutters... in my opinion, all trades.
Low material price = standard, mid-price range = medium execution, high price range = premium execution.
For example, doors coated with foil = standard; solid wood doors = premium.
Tile material price +-20€, tiles half-high and fully tiled in wet areas = standard, tiles everywhere up to 2 meters = premium.
Bathroom: normal bathtub, shower, washbasin and toilet = standard; larger bathtub, larger shallower shower, washbasin and toilet = medium standard; bathtub, floor-level shower, 2 washbasins, toilet (and bidet) = premium equipment.
Faucets and sanitary fittings differ additionally in design, as well as from German brand manufacturers or elsewhere.
Laminate in the living area would be standard, parquet premium.
Standard heating would probably be radiators, underfloor heating premium.
Standard windows would be a patio door, otherwise many windows with sills, premium would be many floor-to-ceiling windows without threshold, possibly with burglar lock.
Entrance doors also vary from basic to premium.
Necessary sockets are standard, some additional and more two-way switches for lights are medium, upwards there is no limit.
Stairs are mostly the "good" beech stair with stringers as standard, then there are upgrades in width and material mix (steel railing) up to freestanding stairs.
Some house providers already include some nice extras in the "standard" (e.g., sash windows or a good front door), otherwise it means: read the specification of services.
You often pay for the medium standard even though the "simple" one is enough for you. For other things, however, you almost always pay extra if they are premium.
Cheap house providers usually offer you a (sub)standard, i.e., an undersupply, often you already have a higher standard in your current apartment... just count the sockets.