I have on hand an assortment of Loctite, which one I use depends on the application. My most go to would be the 243 Blue one. It is oil tolerant and holds up well on my Harley's shovelhead engine. The ones I keep on hand are bolded.
Here's a list I keep handy:
Loctite Application
271, Red: High strength threadlocker for larger diameter hardware.
262, Red: High strength threadlocker for for hardware smaller than that which uses 271, most commonly sold in auto parts stores.
263 Primerless, Red Thread locker Oil tolerant
609, Green: Retaining compound, high strength, for mounting slip fit bearings to shafts.
603, Green: Retaining compound, high strength, similar to 609 but good where the parts may be a little oily.
640: Green: Retaining compound, high strength. Similar to 609 and 603. Lacks the oil tolerance of 603. It has a little greater viscosity than 603.
638, Green: rather thick: Ultra strong retaining compound for assemblies with a marked amount of slop in the fit, min 0.004". Don't try to use this stuff for normal bearings on healthy shafts. It sets almost immediately in the tight gap, and you'll never have the chance to get the bearing into place.
290, Green: Wicking product for thread locking AFTER assembly. Medium strength, much stronger than 242 blue in my experience. Not the correct choice for bearing mounting per Loctite.
242, 243 Blue: Classic medium strength threadlocker for most of our threadlocking applications. 243 is the oil tolerant version.
222MS, Purple: Low strength threadlocker for small diameter or otherwise delicate fasteners.