Here is my ranking:
1. Rejuvenate (best)
This card is flexible, it can do four different things; and one of them is probably what you want to do. It provides green mana if you want it (the one basic color that concentration doesn't provide). Using the basic version of this card to ready Foresters or Illusionists can be a very strong move.
2. Crystal Joy
Crystallize may be a weak card, but unless the source is entirely depleted, it at least gets you a crystal for later. In my experience, I usually have one card in my hand that I know I won't need for the remainder of the round. Why not trade it to get Crystal Joy back? Using advanced Crystal Joy to discard wounds can be quite useful, I imagine. As long as blue mana is available, you can turn one wound into a crystal of your choice each turn.
3. Instinct
Instinct will sometimes be better than Improvisation, but usually not. I often use Improvisation because I need an odd amount of Move, Attack, or Block.
4. Mana Pull
My guess is that this card won't be better than Mana Draw more than 25% of the time.
1. Rejuvenate (best)
This card is flexible, it can do four different things; and one of them is probably what you want to do. It provides green mana if you want it (the one basic color that concentration doesn't provide). Using the basic version of this card to ready Foresters or Illusionists can be a very strong move.
2. Crystal Joy
Crystallize may be a weak card, but unless the source is entirely depleted, it at least gets you a crystal for later. In my experience, I usually have one card in my hand that I know I won't need for the remainder of the round. Why not trade it to get Crystal Joy back? Using advanced Crystal Joy to discard wounds can be quite useful, I imagine. As long as blue mana is available, you can turn one wound into a crystal of your choice each turn.
3. Instinct
Instinct will sometimes be better than Improvisation, but usually not. I often use Improvisation because I need an odd amount of Move, Attack, or Block.
4. Mana Pull
My guess is that this card won't be better than Mana Draw more than 25% of the time.