If it's a soft leather, I'd use the roller foot so you don't get a foot impression and also it'll just glide over easily.

I've worked in alterations for over 40 yrs... The shop I work in now, refers leather to a leather shop... BUT we always used a Walker foot on real leather. it never left any indentions on the fabric. fed the leather thru great...
Sewing anything with leather using a "home machine" means slow going though. I now use only commercial machines.

I forgot about this post so late checking back. Thanks for the replies. It was going to be used to mend a handbag which is not really soft or hard leather, kind of inbetween. Maybe I should get both to see which works better. Don't know what else I will use them on though.
Clare