Units can blow for a number of reasons and you can find once one blows the next one isn't too far behind and then another and another. DGU's aren't really suited to wooden windows due to lack of water drainage and how they are fitted, to be fair I did once see drainage channels and escape slots routered in under the bottom bead but that was 1 window in 25 years in the trade and I've seen, replaced and repaired lots of windows and DGU's in that time, not saying its a reason not to never have wooden frames with DGU's but its something to bare in mind.
I'm a pvc guy, John is for timber, I say both have a place, not all people have the time or money to pay a decorator to stain or paint their south facing windows every two years, so opt for the wipe clean pvc and pvc has come a long way since how John remembers them, don't get me wrong you can still get the basic mitred/welded windows but these days you can get much much more if you want the timber look, not cheap but if your house deserves timber windows but you don't want the hassle of painting every two years then pvc is a no brainer, take a look at residence 7 or 9 and tell me thats not as close to the wood look you'll ever get, just stunning
