I use a 405cx, and an android phone with cardio trainer, and occasionally run keeper for music, bit of radio sometimes.
405 is much better generally, but more expensive of course. 305 is very similar, a bit more bulky.
There are some races you can't use an mp3 player so phones with headphones would also be the same... Okay can ditch the headphones then it gets a bit messy to look at and maybe check pace.
I don't use training centre. Garmin connect is pretty good.
Can't remember who mentioned facebook being important but there is like button for posting on facebook too on the garmin web app.