As I mentioned on this blog, I play a buccaneer in Pirate 101. As soon as I got my first Practice point (the points that allow you to train abilities from other class trainers on your pirate, the first being awarded at level 8), I ran to the Privateer trainer and immediately got the ability to heal myself. This seemed like a good idea at the time, but after a while, I started to wonder if, perhaps, there might be a better option. I decided to see what I could find out, as I haven't read much discussion on this particular topic.
After having looked at all 4 other classes and what abilities I could get with my 4 ability points (2 from leveling up and 2 from completing Prospector Zeke quests), I bought the first 4 abilities from the Witchdoctor class trainer (besides bonus to Staffy weapons). The thought process was that I could turn what was essentially a paladin (healing tank) into a dark/death knight (black magic/poison tank). Now, I'm only level 15 (going on 16), but this seems to work a lot better. The Privateer ability that I had been using the most, an multi-target bomb drop, was replaced by a multi-target magic spell, the healing ability was replaced by a drain-style self heal, and the buffs I never used were replaced by direct damage spells and a debuff. For my play style and level, this seems to be working out a lot better. What I always hated about the healing spell was that it didn't heal for a whole lot, since as a buccaneer I don't have very high Will, and I didn't like wasting a turn with one of my heavy hitters in order to heal a companion. This way, I can just heal myself while doing damage and the battle is over faster, so I don't take as much damage anyway.
It may be different at higher levels, but I don't see any downside to using the Witchdoctor skills. Also, I couldn't see much advantage in subbing swashbuckler or musketeer. If anyone has any compelling reason or awesome strategy that involves Bucc/Musk or Bucc/Swash, let me know!