Toughness is almost always better early on, from then it depends on your playstyle.
Toughness is an up front bonus. Durable is a bonus that is only useful when you are on your last healing surge and wish you had 2 more. Durable may mathematically give more HP, but only if you use every single surge. This will only happen if either everyone in the group has durable, you're the defender with plenty of leaders, or your DM likes to push you to the very limit. Also, maybe you have other ways to spend your surges, but then we're no longer talking HP to HP. Take durable to spend on those powers, since you can't spend toughness in this way (ok, maybe, there are some powers/feats that do damage to you)
Durable may be better on paper, but I always feel better with the upfront hp, higher bloodied value, higher surge value, and that extra margin between life and death.
Toughness is an up front bonus. Durable is a bonus that is only useful when you are on your last healing surge and wish you had 2 more. Durable may mathematically give more HP, but only if you use every single surge. This will only happen if either everyone in the group has durable, you're the defender with plenty of leaders, or your DM likes to push you to the very limit. Also, maybe you have other ways to spend your surges, but then we're no longer talking HP to HP. Take durable to spend on those powers, since you can't spend toughness in this way (ok, maybe, there are some powers/feats that do damage to you)
Durable may be better on paper, but I always feel better with the upfront hp, higher bloodied value, higher surge value, and that extra margin between life and death.