Like PamMo, I, personally, like the floor plan of the North units v. the South for families, even though the south side is roomier. The North has a layout similar to adjoining rooms at a hotel. Each side of the lockoff has a door leading out to the common hallway, but there is also a door between the two units that you can prop open to make it seem like one unit. The South has a private vestibule that is shared between the two villas. And the door shuts behind you automatically, so you need to keep your key on you at all times. Certainly not how I'd like to be positioned with young kids, especially since each side has its own stove and lanai, and the hallway door can be locked (via a metal plate) from the inside.
If view is important to you, and/or if you will ever need to rent your unit, then my advice is to buy the best view you can afford. I rent a lot of villas and timeshares, and I exclusively target OF units that are reasonably priced. (Note that competition is fierce for rentals, so don't expect to make a killing when you literally have 1000 other units for rent at the same complex, but you should be able to make a small "profit" (over MFs) if you buy OF or OV.)
For OF, south is going to cost you about $5k more than the north, but the views are superior and lanais much roomier. On the south side, only OF comes with a lanai on both sides of the lockoff. (OV and IV studios have juliet balconies, which IMO are useless.)
If you are eyeing OV, I'd buy north side ONLY. If I wanted IV, I'd rent. No need to buy.
If you plan to lockoff and use each side separately, I'd target the North ONLY because you'll get a full lanai on both sides. OF is still very nice. I owned one and loved the views.
If you love to cook, consider the south as it has full ovens.
Ohanamama speaks of the OF deluxe rooms, which have great views, but beware that their MFs are about 25% higher because of that extra space. Deluxe units also have beautiful light because of an extra window, but they are also hotter.
It's also worth noting that the County of Maui has a vendetta against WKORV. Long story. Owners were assessed ~$650 (IIRC) for "back" property taxes, which Maui assessed against WKORV ONLY, in retaliation for a lawsuit that Westin filed against the County re property tax valuation. Owners may or may not ever see that money again, but realize that in this pissing contest, owners stand to lose the most.