Output impedance changes with each different process. But in general triple cascoding has no advantage for BJT's but it can boost the output impedance of a MOSFET stack. Also there is the deal of base current but it can be compensated. Still for fast mirroring like differential to single ended conversion I believe that BJT's have better performance as always in fast circuits.
If you are asking other than cascoding, they both have lousy performance. In modern technologies they really have quite small output impedance. So it's required to take precautions. In this area MOS is kind of better as simply increasing its length increases the output impedance while in BJT's it's harder I think but I do not know for sure which parameter of BJT can be easily changed and affects output impedance.