I don't know how many older lenses you've tried but some tend to be a bit funky wide open and although his may not be an issue with some subjects and compositions it can lead to a distinctive look with others that can be a bit Marnite. I have a 50mm f1.2, several 50 f1.4's, 85mm f1.8/2 and a 135mm f2.8 and 35 and 50mm f1.7/1.8/2's I don't think that any of these give the smoother bokeh look you'd get from a good modern lens but they can certainly give a nice look if you're careful with your use of wide apertures and compositions. One option is to stop down a bit and reduce the camera to subject distance. This may give a smoother look without the more funkiness you might get wide open.
Sorry if you already knew all this.
I don't really sort my pictures out and I do forget what gear I used for what picture but I'll post a few examples I do remember and like... The first was taken with a Minolta Rokkor 50mm f1.2, I think at f2, the second is the Rokkor 135mm f2.8 at f2.8 and the last was taken with a 24mm f2.8.
One thing I do think is maybe often and even maybe largely overlooked is the look you get when stopped down a bit. It's something that doesn't seem to get talked about much and I do think that some lenses give a really nice look when stopped down a bit. It's something to maybe think about anyway.
If you're interested in a particular focal length it may be worth googling for reviews and samples.
Good luck choosing and have fun!