I don't understand your question. Dimensioning a transistor is one of the most complex operations in design.
Larger transistors suffer less from matching,
smaller transistors are cheaper in area and have less parasitic capacitance,
shorter transistors have a lower on-resistance, but also a lower off-resistance, wider transistors can lead more current but provide a larger gate capacity, which limits their switching time ... and so on ...

The smaller you CAN make your transistors, the cheaper your chip will be in the cost of area. However, making the transistors smaller might increase noise, so that you will have to provide more bias current, which will be expensive in terms of power consumption ...

As you can see, there's no "general" answer to your question ...
(and we didn't even talk about matching, temperature, ...)