Unless you plan to do a lot of nature stuff, I would suggest the Rodney Bay area. We spend the winter here now, there are loads of bars and restaurants within walking distance. St. Lucia is one island where all inclusive is not what you want to do. Some hotels I would recommend are any of the Bay Gardens property's except Marina Haven, Coco Palm, best breakfast of all the hotels, Harmony Suites is also good although I haven't stayed there personally. These are all a short walk to the beach and near the bus stop. The bus system on the island especially up north, is fantastic; very easy to get around. If you decide on an airbnb make sure it's not up in the hillside.
Harbor Club gets good reviews but is a longer walk to the beaches although there is a bus stop right out in front.
When our friends come to visit we rent a car for a couple days and drive to Soufriere area for the mud baths, waterfalls and tet de Paul trail hike. If you want to climb the Pitons you have to leave very early in the morning to be at the trailhead by 730 at the latest.
Friday night street party is not to be missed, great time.
We had friends come for their first time last month, they usually go to Florida but after just 5 days they booked a month for next year.
To put it in perspective, they stayed last week on Amelia Island near Sarasota and what they are paying for a week there is just about the same as they will pay for a 2 bedroom townhouse in a gated complex with a pool for the month, they will be about 10 minute walk to the beach. We have a huge 2 bedroom 2 1/2 bath apartment huge kitchen, dining area and living room for less than $100 US a day. We are in a residential area and 10 minute walk to the stores, 20 to the beach, all on flat ground.
If you are looking for a high end, don't often leave the resort location some very posh properties around the Soufriere area, Jade Mountain, Sugar Beach, Hotel Chocolate are a few.