Garmin 201, 301 or Garmin 205 or 305?

I don't own any of them but have researched.  So, take this with a grain of salt.  The new units have better GPS reception technology allowing for faster sync and reduced signal loss.  That alone is huge IMHO.  I think the 305 changed HR protocols as well, allowing for better performance.

Water...I think the consensus is that they are "supposedly" able to go in the water, but nobody has the guts to do it.  I've seen people put it under their swim cap in the back of their head to protect it, and it works fine.

Swimming...a stack of pennies, move one off the stack of "x" until you're done.  Divide the workout in half and count up, then down.  Standard chorograph watch...start the chrono and hit the lap button at each wall or every other wall.  That works for me.

Correct, but as I said, most users I've talked to are skittish about doing it.  Oh, I forgot, the 201/301 is very long and rectangular, while the 205/305 is smaller, kinda square, and more comfortable.  Nicer display in a smaller package.  Still much larger than a watch, but not AS LARGE as the previous iterations.

The 205/305 is very large.  I recommend trying one on before you buy it.  I have very small wrists and I couldn't comfortably wear one with either of the bands that comes with it.  I could easily wear a 201/301. 

• Heart rate monitor and chest strap. The HRM seems to be farmed out to CardioSport (their coded chest straps work with the 301) and many people have experienced problems with the HR reading coming and going. Note that many more also have never had problems, but enough have complained (and Garmin did change with the 305) for me to believe it is somewhat problematic.
  
• Advanced Workouts. I'm assuming this works as does in the 305. You can setup any kind of workout you can imagine using any type of guide (ie HR zone, time, distance, calorie burned, etc) for each step.
  
• Multisport functionality. Again, I'm assuming that this works the same as the 305. Allows to setup differnet HR and speed zones based on sport (Cycling, Running, and Other). Also has an auto-multisport mode that you configure the sports that you will be doing as one activity (ie triathlon=other, bike, run) and then specify whether or not transitions will be included. Then each time the lap button is pressed, the next sport (or transitio) is automatically started. I've had problems with this by accidently pressing the lap button and messing it up.
  

• A better, more sensitive GPS receiver.
  
• A different HRM (chest strap and transmiter/receiver) from DynaStream
  
• ability to add a wireless speed/cadence sensor. The speed is used from this when no GPS signal is available (most useful when on the trainer).
  
• a different "watch" case. Most like it, but I prefer the 201/301 form factor.