Sunshine or Lake Louise are both great hills for mixed groups. I'd say Sunshine is a little friendlier for newer skiers as the runs tend to be shorter, and there is much more moderate terrain. Lake Louise offers a lot of "better" terrain for more advanced skiers, but the snow often is poor, while Sunshine can sometimes offer a little better snow.

Sunshine does have some really awesome skiing if you know where it is. Delirium dive (need a partner), South Chutes and Hells Kitchen on Goats eye offer some stellar double black terrain, and there is some fun black terrain in Goat Chicken Gulley on Goat's eye and the terrain above Teepee Chair.

You really can't go wrong either way though, both mountains are pretty good as a whole. Ultimately it will really depend on snow conditions. Early march is likely still good, although late march can get a bit "spotty" in terms of conditions.