Unless avios-poor, I would always upgrade to F on a daytime flight or a long overnight, maybe not on a red-eye from the US east coast. The extra space (especially on an A380, which has the largest F suite in the fleet) and quieter cabin aside, I personally prefer dine on demand, which is not possible in CW. On LHR-ORD, I would do this in a heartbeat for 18K avios. Only caveat from me is that I am also yet to fly CW in BA's A380, only been in F to date. I've experienced plenty of CW in other aircraft and also had walks through CW on the A380, haven't seen anything that would change my mind.
Increasingly I find myself booking F when flying BA metal long haul, partly to avoid CW and partly because ex-UK, the A class fares can provide a semi-flex ticket at what in some cases has been not much more than an inflexible I-class in CW. The extra TPs and avios are a bonus (though slightly OT as the OP is asking about UuA)