Synthetic jacket vs fleece

[Kukkudrill]

I have a mid weight (I think) fleece weighing about 400g and a Haglofs Barrier Pro II synthetic insulated jacket weighing 320g. I assume this is the sort of jacket the OP has in mind. It is a lot warmer than my fleece so in spring and autumn I would only use it to layer up over the fleece when I stop walking.

[christer]

I use an arcteryx atom lt jacket. It is warmer than a mid weight fleece outright plus it is windproof so performs better. I estimate it to weigh only about half of a midweight fleece and packs down to about a third of the size.

When on longer hikes space and weight are extremely important but ofc if you are just walking the dog or similar it comes down to personal preference I guess.

With a merino wool baselayer and thin tech top over the top I have worn the atom as outerlayer at minus 7 degC, with it being perfectly warm whilst moving. When stopped I usually have my PHD down shirt to throw on underneath if necessary. 

I don't use fleeces anymore but they are normally substantially cheaper.....