I would (and did) go for the secteur.
The secteur and synapse are what are know as endurance road, as in they are a bit more upright and a bit less weight on the wrists. The others are more along the line of "racing" bikes.
If you are in the physical condition to be able to use a racing bike for your rides then choose whichever you like, but for me, being a bit older and fatter Im glad of having a more upright position!
As your have written "I rie for fun, fitness and fat burning" under your avatar I would suggest you look towards the synapse or secteur, as they should let you keep riding further for longer.