I went with Amoonguss cos it has better stats than Alomomola and a good support movepool. Amoonguss makes a great wall, with some good moves like Toxic and Rage Powder. It even has Spore, which is one of the best sleep moves ever, making it easy to catch Pokemon too.
Alomomola may look beautiful, but its stats didn't cut it for me (way too much focus on HP!) and its movepool isn't all that great AT ALL.
So, that's why I picked Amoonguss.