I prefer just the full form, [name_u]James[/name_u], but I really do like [name_m]Jimmy[/name_m], too! It’s just such a friendly nickname and has an iconic feel to me, like [name_m]Tommy[/name_m]. Pretty much every [name_u]James[/name_u] I know goes by either [name_m]Jim[/name_m] or [name_m]Jimmy[/name_m], so it definitely works 