I grew up as a wee lass in Scotland believing that "neeps" was short for "turnips" and that turnips were the big purple veg with orange flesh. It wasn't until I moved to England that I realised that swedes and white turnips were different vegetables!

Anecdotes aside, I've always eaten haggis with mashed swede. I find the sweetness of the swede flesh goes with the spiciness of the haggis.

incidentally, it is my understanding that you cannot buy a proper haggis in the US because they are not allowed to sell the lights.

Not sure when a swede turns into a turnip, both are neeps! Try with a beef olive filled with haggis, for something different. You can get sliced haggis, same as black pudding etc., to save wasting a whole haggis, if only filling a couple of olives.

actually, neeps are swedes...

http://www.guardian.co.uk/lifeandstyle/wordofmouth/2010/jan/25/neeps-swede-or-turnip