I like them both, they have their place.
As I've said elsewhere on here, I wouldn't put anything on them that I'm not happy for the whole world to know, if you follow that principal you can't go wrong.
Twitter has been really useful for grumping about stuff to big companies and it getting sorted really quickly.
Virgin Trains' Twitter desk is really good, they're really helpful on there and more than once they've been able to arrange seat reservations for me via Twitter when the people in the Travel Centre told me "computer says no".
Neither are a forum though and couldn't replace one effectively though.
One thing I will say (actually, that's a lie, I'm going to say loads of things over the months and years) is this. Having been so nicely welcomed over here by Malcolm and seeing how well put together it is and how well it is run, I think perhaps its a tad impolite be bemoaning the demise of the old forum.
The way I see it, we've only benefitted in the long run by being sent in the direction of this forum so by all means, lets give the old one some stick and reminisce about all the faults that it had but I see no reason to express sorrow at it's demise, what we have now is much better.