On APSC, the DA15ltd is unique to the Pentax system.
Tiny (hence very portable), very flare resistant, and the starburst (for the non-HD version)
I used it a lot before my switch to the K1.
Add in simple vertical frame panos and its versatility is further increased.
---------- Post added 01-03-2021 at 06:45 PM ----------
On the K1, the Ltd that is most versatile is certainly the FA31ltd.
A decent smallish sized for a fast f1.8 wide lens, superb reportage focal length and very flexible natural landscape focal length.
The amazing draw of the subject when slightly stopped down is icing on the cake.