My two penneth....
I'm antique restorer and French polisher. It's what I do. I almost bore myself telling people this, but old antique furniture, quality wise, stands head and shoulders above most high street stuff you can buy today. Both the construction methods and materials are generally far, far superior. Over the years we have repaired various items made by some of the names mentioned above, even the ones presumed to be top quality, and the methods of construction and materials used are often shockingly poor. 'High end' sofas made from Sterling board or MDF for the frame materials, all stapled together without so much as a proper wood working joint anywhere. Contrast with Victorian and Edwardian furniture, made from beech for framing, quality deal or pine for carcasing and mahgogany, walnut, rosewood and oak etc for the show wood and there's no comparison. Partly, this is born out of necessity of course. All of the aforemention timbers have become scarce and as a result very costly, so today's manufacturers are compelled to use inferior timber types, or, more usually, MDF, chipboard and cheap, crappy soft woods.
There is a big but though. Antique and vintage furniture almost always comes with inherent character, or 'patina', as it's called in the trade. This will usually mean at the very least, small dings and dents, perhaps some scratches or fading here and there. It's actually much prized among the dealers in higher end, top quality Georgian and Victorian furniture and its actually very easy to over restore(and thus devalue) these items by removing these marks. If any of these usually minor discrepancies are likely to bother you then you might be better sticking to brand new, but just know that you are likely to pay much, much more for something probably far less quality and it will depreciate like the Rouble.
As previously mentioned, local auction houses are brilliant and there's an element of fun in the chase, assuming you like that type of thing. Given that 'brown' furniture has been out of fashion for some years now, there are still some fabulous quality pieces selling for an absolute song. An example: I recently bought a gentleman's compactum wardrobe for my own home; hammer price £150, plus buyers premium took it up to £181 for a fantastic piece of solid walnut furniture that would easily cost in excess of five grand to make today. Another plus side to this is that as long as you buy reasonably sensible, you are unlikely to ever lose much money and most things will retain nearly all the cost price you paid, and quite possibly even appreciate in coming years. And at the risk of over selling this a little now, ( like I haven't already
) you can always pat yourself on the back for your green credentials in reusing something that would otherwise mean more trees being cut down and eventually more landfill.