To answer the good/bad question first, it depends on what you are looking for. The two islands are as different as day and night. St Maarten offers beaches, high-end shopping, gambling; Saba has none of those things. Saba has great diving, beautiful hiking trails, and a laid back, friendly, and crime-free atmosphere.
As far as dive operations, see this thread:
http://www.scubaboard.com/forums/lesser-antilles/483070-saba-anyone-dive-saba-divers.html It has a lot of information about what you can find. For accomodations, there are a few hotels that offer anything from an eco-friendly experience (El Momo), to upscale amenities (Queen's Gardens). There are also a range of cottages available for rent. You can get more information from the Saba Tourism web site (
http://www.sabatourism.com/).
Windwardside, where almost all the tourist accommodations are, has several restaurants, most of which are surprisingly good and not super expensive, given the fact that virtually all the food must be brought in by ship. If you stay in one of the cottages, you also have the option of doing at least some of your own cooking.
If you want help sorting out what's what on Saba, you will find that Lynn at Sea Saba (
http://www.seasaba.com/) is the best-connected source of information for where to stay and what to do on the island.
How to get there depends on your timing and preferences. WinAir flies there several times a day, and there are ferries that run several days a week.
I hope this helps.
Larry