I took the plane in 2008 and it was a NIGHTMARE. My memories are of paying the excessive excess baggage allowance, humphing heavy bags, queuing, expensive taxis... the list goes on. Driving to QM2 last year was easier, but then we had to contend with expensive Southampton accommodation and parking.
Same! The usual Cunard transfer package from Switzerland to London then by bus to Southampton is rather uncomfortable, unfriendly, expensive, and the baggage allowance is much too low.
It may sound weird but we now prefer to drive all the way with our own car, including a ferry crossing between Caen and Portsmouth, and the bit of the left-hand driving between Portsmouth and Southampton. It's more relaxed and less hassle, and the parking facility at the Ocean Terminal in Southampton is nice and easy...
Cunard also offer parking (it's usually free for the length of the cruise, depending on the 'Offer' at the time of reservation) at the new terminal.
...well, as far as we are concerned as Swiss guests, such offers from Cunard don't seem to exist

But still, much better than the "nightmarish" flying way.