My 5 favorite lenses by length:
S-M-C 17mm fisheye takumar - With a lot of light so you can stop it down so it gets sharp it produces nice images and once you figure out how to use the distortion is is fun to play with
SMC A 50mm f/1.2 - This lens made me fall in love with 50s again even on crop sensors with how it renders texture even though I didn't like any of my other 50s on crop sensors. Even wide open it is fun with the softness and in hard lighting conditions the glowyness so why not own those aspects is such situations. When stopped down it has a rendering similar to the 77ltd.
SMC 77mm ltd - got it because initially I didn't have anything between 55 and 135 and figured why not get it instead of an 85mm. Again I like how it renders texture but the colors are also really nice and does give that nice subject/background separation for that 3D effect.
Sigma 300mm f/4 APO Macro - I used this lens for a long time as my goto deep sky object (DSO) astrophotography. It is sharp and has very low distortion plus doesn't fringe or halo. Add in that it is close focusing so it give a 1:3 macro and I still like it for flower closeups. I will often have it on my camera while walking through the forest.
SMC A* 400mm F/2.8 - If you have a need for a long lens at this length and the huge slab of glass in front will do more good than harm you can't go wrong. Here
is a shot I took with this lens at its worst wide open and still coming down in temperature in the most punishing type of photography that shows all of a lenses defects. Waiting for it to come to temperature and stopping down 2/3 of a stop and it is perfect. For chasing DSOs it is ideal for the big ones. Things like Andromeda will fill the frame and you can get nice framings of others as well.