Why not use both?
Only reason I wouldn't use both is because, the Resistance passive is nice, also the Armor passive is in no way worth giving up, and the healing passive is amazing, X Health for every point of spirit is awesome especially combined with a MoH Spirit Dumb.
I used to use the healing passive, but I found it to be not so useful as my health pool increased. So I switched over to using the -25% damage, which is why I now use both. It heals for what, 62 per point of healing, so thats 3k every MoH activation, which isn't bad, but when you have 30-40-50k hp, gets kinda negligible.
I guess it would be time to maths. You'd need to calculate spirit expenditure vs damage taken and such.
If you are on average, spending say 50 spirit every 3 seconds, that would be 3k healing or 1k hps. If you are taking 5000 dps from monsters, the 25% less damage passive would give you a 1250 dps reduction for instance.
I'd think the further you go, the more the -25% damage > the healing. The heal value doesn't scale past 62 per point, and your spirit generation isn't going to scale at all at some point. However, monster damage does scale, meaning that the harder monsters hit, the more value the - damage has and the less value the heals have.