Contrary to what you will read in almost every guidebook to Florence, the Ponte Vecchio is not a very romantic place to be, especially at sunset. The reasons are several:
1) every man and his dog crowds the bridge at all hours of the day and evening making your romantic seem like it is taking place in a stadium;
2) given that you will need to wait your turn to stand by the edge with your chosen one in order to gaze on the sunset and kiss, some of the novelty value will wane; and
3) most importantly, because the Ponte Vecchio is more beautiful to look at than it is to look from! The light in early evening gives a whole new charm and definition to the old bridge. Oarsmen and sculls glide underneath as the water reflects Michaelangelo clouds, azur skies and golden red hues.
From the Ponte Santa Trinita (the bidge of the holy Trinity), you can watch the Ponte Vecchio in all its splendour and then, turn towards the sunset and . . . alone without a throng watching, offer a gentle, romantic and truly unique kiss to your love. She or he will be impressed by your deep knowledge of Florence and be all the more attracted!
If that doesn’t work, on one side of the bridge begins Via Tornabuoni and all the most expensive fashion shops in Florence! Now, that is romantic!