Good question! Here's the answer:

I had 2 skill points to use.

Option 1: Lower the casting cost of REVIVE from 20 mana to 10 mana. In addition to the ability to revive dead people, REVIVE also provides +1 mana regen for one minute. When it costs 20 mana to cast, it provides 40 mana every minute (60 – 20). If it costs 10 mana to cast, it provides 50 mana every minute (60 – 10).

Option 2: Raise FORCE SHIELD to level 2. The armor buff (+40) would be so small as to be useless, and goes away after taking 35 damage, which is one hit from any enemy when you are level 47. The +1 mana regen seems useful, but has a whopping 45 second cool down; but to make calculations simpler, let’s assume I would cast once every minute. If so, it would provide an extra 20 mana/minute (1 mana per second for 30 seconds minus the 10 casting cost). Combine that with REVIVE at level 1 and you have a total of 60 mana/minute regen (40 from REVIVE calculations above + 20 calculated here). If you actually were on top of things enough to cast it every 45 seconds instead of every 1 minute, it would provide slightly more. HOWEVER, 50 mana/minute by raising REVIVE to 3 rather than 60 mana/minute by cobining REVIVE level 1 and FORCE SHIELD level 2 is a better tradeoff for me. Why? Because (1) I do not have mana regen issues very often and (2) My 8 skill slots are already filled up and there is no sense in training a skill that will rarely if ever get used because I know I will not take time to swap it in to use it.

Option 3: Raise PROTECTION to level 2. It is my opinion that Protection at level 6 (+60 armor) is nearly useless. At level 2 (+20 armor) it would do nothing. And again, my 8 skill slots are already filled up with other skills. I would never take “swap time” to use this skill.

Option 4: Raise PAIN to level 3. It would increase the initial damage output from 2-8 to (5 on average) to 4-12 (8 on average). It would not affect the AoE damage. I am disappointed by how little damage is increased by putting points into this skill. Still, I use this skill A LOT, so this would be a decent option. The main reason I use this skill is for the 3 second stun, which is the same no matter at what level it is trained. By my calculations, it does 37.5 damage per minute at level 1 (60 seconds in a minute/8 second cool down * 5 point average damage). It would do 93.75 damage per minute at level 6 (60 seconds in a minute/8 second cool down * 12.5 point average damage). The damage is 5 – 20 at level 6.

Option 1 and 4 are both viable options. And in fact, I plan to pursue both of them. I chose to raise REVIVE to 3 first to get the extra mana regen. I see no benefit in raising it further. I am now level 48 and raised PAIN to 2. By the time I reach the current level cap of 51, PAIN will be at level 5. And that is where things will sit until the level cap is raised further.