It might be worth looking into rum as well if they like sweet. Probably not most Jamacian ones though.I'll say you're starting from something that's fairly sweet, and as for smoothness... honestly not too difficult to get smoother than JD (though it's not as bitey as Jim Beam or ryes/Canadians IMO). So far some of the smoothest whiskies and such I've had the pleasure of drinking are Tomatin Dualchas (scotch, and usually not much more expensive than JD because for some reason Tomatin is criminally underappreciated) and Willett Pot Still Reserve (bourbon, bit pricier than JD but worth it if you want something bourbony).