I just upgraded from the 170cc to the 190Bay. Primary reason: Wife & Kids. I've got a 3 & 6 year old and the bigger boat will accomodate all the "stuff" they like to bring along. While I loved 170cc the storage is somewhat limited, especially if your taking 5 people out. I also feel the wider beam is a big benefit, the extra room will help every one get around on the boat and make it a little more stable. So, I vote for the 190Bay if you can afford it. But thats the catch, if the 190Bay is a stretch financially, you might enjoy the 170cc and the extra savings it will give you. I don't feel boats should stress you financially on the purchase (they will do enough of that afterwards)
-Kevin