if you are looking for a fast lens and don't mind the size, the 1.2 nokton is a great lens, very resistant to flare and a more modern look vs the pre-asph lux. also, a tad faster.
but if you're looking for a slower but sharper lens, maybe the 2.8 biogon could complement it well.
having lenses with very different looks in the same focal length is useful sometimes if you don't mind switching, for some situations some are best, some are worse.
i am not a big fan of lens flare, so i like flare resistant lenses. but i also like low contrast, old looking images... so having lenses in both directions is nice when you want to achieve a specific visual character.
i like the v4 cron a lot, it's tiny, has nice color tones and i dont see any distortion, but it can flare a lot (purple toned), the square hood helps but won't 100% keep it flare free.
the 1.4 nokton is quite versatile, but since it's pretty much a pre-asph lux copy, it'd be redundant.
the f2 canon ltm is a very nice lens, i've been shooting with it these days, haven't got many frames with it but it's tiny, light, sharp, renders nicely. min focus 1m, though, and odd filter size (i dont use any, so not an issue for me).
1.7 ultron is a very nice lens, a tad faster than f2, but sharp, resistant to flare (i can use it even without the built in hood and it won't flare), good ergonomics but not as tiny as the others. very nice bokeh.