Well now you got me to thinking.
Background - I use the Intergral Designs SIL Cape weighing 5.5 oz, it just covers my pack. I like it. I see plenty of rain, moderated winds, also carry a wind jacket, mix of easy and very tricky terrain, do not use a poncho as shelter and don't want to (no offense).
Your question got me to listing features or rain gear that may be important for the conditions I see; rain protection, condensation, draftiness, gale wind performance, walking ease, scrambling ease, chore ease, pack coverage, versatility, weight, elimination of other items and social acceptance. I weighted each of these as to importance (rain protection = 5, social acceptance = 1). Then I estimated each items score - for my use.
I thought to validate my own preference. The score: Poncho 128, jacket 128. Surprise!
For mountain hiking I think the jacket wins based on high wind potential and scrambling. Poncho wins if you consider expense.
I've logged several hundred miles in this poncho, been in 36F 45mph steady wind (Lake Superior). I batten down the poncho in wind, wear a wind coat underneath in cold windy conditions for some arm protection/warmth, have used it as a wind shelter for cooking, etc. I hate being clammy but am thinking of the times that I could't see my footfall in tricky wet terrain. Comfort. Safety. Weight. Crappy pack covers. Now what?
I've got constipation of the brain. You owe me a beer.