Attunement=Faster casting speed, more spell slots and some agility(and HP?) ADP just boost agility, HP and some fairly inconsequential stuff. Obviously Attunement would be the better choice for a caster.

Does attunement increase agility?

Attunement also provides, albeit smaller, increases to your Agility stat. Agility is hard capped at 120. It is possible to raise agility up to 120 by having both Adaptability and Attunement at 99.

Does attunement increase spell uses?

Notes. Attuning multiple copies of the same sorcery, miracle or pyromancy will stack the number of uses; however, this will not change how many uses one gets per slot. Most spells require only one Attunement slot.