The #10 adjustable has to be one of the most enjoyable nibs to play around with. It's not too fussy about paper in terms of scratchiness except the usual story about 'bleeding'.

One of my favourite nonWahl nibs is a small Pilot nib that I got in a vintage Italian safety pen. It's super flexy for it's size and I often use it for letters and notes when I want a bit of 'flair'. The #10 nibs write too 'big' for a letter.