OK, I have both so I'm cheating.
I like the 201-2 far better than the 15-91. So if I had to choose I'd take the 201-2.
~But~ I don't do FMQ. So the larger arch and top loading bobbin of the 201 is much more to my liking.
~But #2~ I might take up FMQ without prior notice, so I'll keep 'em both.
That sure didn't answer your question did it?
OK, I like the larger arch and top loading bobbin on the 201-2.
I dislike the end loading bobbin on the 15-91 as I have larger hands than the folks way back when had when the machines were designed. I find the end loading bobbins of the Singers and other makes to be awkward and clumsy.
I live with it, but when I'm sewing I use the machines with top loading bobbins far more than the end loaders.
Joe