My personal preference is to wear a solid-coloured, regimental, or club tie with a kilt. I usually only wear a tartan tie for those times when I'm not kilted but wish to show my affiliation.

The one exception would be as Jock Scot points out - "It is quite acceptable to wear different tartans of the SAME Clan. My Clan has over a dozen, for example. It is not acceptable to wear tartans of DIFFERENT Clans."