Akira, the Mitutoyo objectives are really good. Plus they allow a very decent working distance despite their high magnifications. However they are "infinity corrected" thus must be combined with another optical component to focus, and of course the magnification for all intents and purposes is fixed. I have the 5X and 10X Mitutoyo objectives.
I also use some Olympus macro lenses made for the OM system, 20/2 and 38/2, the latter being ruggedised to allow it being brought into the field. The vintage Macro Nikkors see some use, too. Mostly the 65mm f/4.5, on occasion the 35/4.5 Macro-Nikkor.
This season I have used the Laowa 25mm f/2.8 Ultra-Macro lens on a regular basis as it exhibits good quality, and is small thus making less demand for an extended support structure. It's not perfect, but nifty for my purposes and the 2.5-5X magnification range is spot on for most of my subjects. Putting a CPU inside helps secure EXIF data which is helpful for fine-tuning the setup.