South of St Lucia offers some great attractions including nice beaches, great Scuba diving and snorkeling, a number of beautiful hiking trails, waterfalls and other unique attractions like the Pitons and Sulphur Springs Park. Although the South is gorgeous it is extremely quiet with limited dining and nightlife options.
Splitting your time is a great option as it allows you to see all that St Lucia has to offer, the Pitons and what the South has to offer and allows you to see the more populated North end as well.
The north is also very beautiful and picturesque but it depends on you and what you want from your holiday. If you want some nightlife, nice meals out and something more upbeat while you are there, then the north is where its at!