I'll agree with what Zaft said. I'm sure you'll get people who come in here and argue about how good spell speed is, but take a few things into consideration when aiming for spell speed. A lot of your healing can/will be done with regen/medica2. Since regen is instant and medica lasts 30 seconds, then more potency in their heals will be best for those skills. Spell speed will not help those spells as much.

There will also be times when those "Oh *instertwordhere*" moments happen. In that instant, some people will say that it is good to have spell speed. While I somewhat agree with this, when you play with a group of people you know and trust, then those moments kinda stop happening. So if you like to duty finder or party finder a lot then you may want to go for that because you don't know how other people play. At the same time as well, you won't notice a big difference in casting speed. The same can be said about stacking all determination.

Honestly, if you want the most bang in your heals, go for determination. If you would like to get that heal off 0.1-2 seconds faster then grab spell speed. Whatever you decide, if you do your job and do it well, then you did it correctly. I know scholars who can equip whatever they have on whitemage and perform great. It is great though, to get a cure 2 off just as death sentence hits so you get the heal, but not affected by the debuff. So work on timing your heals just as damage happens.