Super tech challenge – go to Stainburn, long XC trail – go to Dalby. Both good, both different, each to their own and all that 😎
Haven't been up but quite a bit of Stainburn is in woods so it should be sheltered. There has been snow in Leeds recently but temps have risen and a lot has melted off. More will lie at Stainburn given it's out in the country / higher / colder. I think I would chance it.
Boulder trail is fully armoured construction (in theory, there are some muddy parts) and whilst I appreciate it's always nice in the sun the place is rideable year round. Some people find it slippy / greasy but not so bad IMO.
Go and hate it and you can easily salvage a ride by taking up Rob's suggestion of Scar House (providing you're out earlier in the day).
"Big" sussers can be more hindrance than help on the Double Black (although lovely for the Descent Line). Shorter travel FS or LT HT are probably ideal. All intended to be rideable on a HT, rock whatever you want though as we've seen all sorts there. It won't be the bike that holds you back 😉
Usually people around throughout the day as well. Pads and a bash ring can help reduce the fear factor and big ring grinding common on the trails.
Norwood (other side form the car park) is worth a look and there's a rough map somewhere in the Stainburn section of the SingletrAction.org.uk forum (main site has been down with server problems recently, forum still OK though). Ask on there for more locals advice although you've had a few respond here. Norwood is likely to be much muddier and the trails more "old skool" following felling work and resulting disturbance.