Having had an 07-plate Panda as a daily driver for a while (the 500 and Panda are very similar inside) - I found I was constantly knocking and rubbing my left knee on the centre console...plus, it's a very 'sit-up-and-beg' driving position compared to the low-slungness of the 133...
There's an Abarth 595 parked up where I live and it sounds great as standard compared to my 133 (haven't played with the exhaust, yet...), but there are some pretty awesome mods out there for the Twingo, so it's much of a muchness in that department...
As the above have said, try both and choose the one you feel suits you.