There can be only one...jacket that is.

[Zardoz]

I find myself both agreeing and dis-agreeing with most of the posts in this thread..I think if you can initially only afford one jacket, I feel like a charcoal tweed jacket and waistcoat set is a more versatile way to go.

I agree that the typical black barathea shiny button Argyll jacket and/or waistcoat set is quite versatile, it can go from daywear to semi-formal with the right accessories etc... But honestly I really feel like the shiny buttons (which could be changed out) make it look a little 'fancy' for some settings.
I feel like a charcoal colored tweed set is really more versatile overall. It won't cut it for black-tie, but it can go from more casual daywear to evening events where a dark suit or 'business formal' is expected. And the color goes well with most things.

I have both styles, and I wear the charcoal tweed quite often. But since I got a mess jacket for more formal stuff, maybe 3 events per year, I hardly wear the black Argyll at all.
I guess it depends on how often you are going to attend the more formal events.