Note: This is with (3) points in Improved Renew (which makes Renew 15% more efficient).

Renew(3): 201 hp over 15 sec for 105 mana = 1.92
Lesser Heal(3): 143-165 hp, 2.5 sec cast, 75 mana = 1.91
Heal(1): 304-351 hp, 3 sec cast, 155 mana = 1.96
Power Word: Shield(3): Shields 161 hp for 130 mana = 1.24

Renew(3) would probably only be 1.67 without the +15% specialization. PW:S(3) will get a 15% boost once I spend 3 talent points on it (boosting it to 1.43). And sometime before level 40, when I have 5 points in Mental Agility (+10% efficiency for insta-cast spells) that will boost PW:S(3) and Renew(3) to:

PW:S(3): 1.56
Renew(3): 2.11

Which will make Renew very worthwhile.

At level 22, I get Heal(2) which is 429-491 for 205 (2.09).

Level 26 gives me Flash Heal(1) 258-314 for 155 (1.66). I also get Renew(4) which should be 282 for 140 (2.01).

Level 28 gives me Heal(3) which is 566-642 for 255 (2.22).

Level 30 gives me PW:S(5), 301 hp absorbed for 210 mana (1.43) but I'll have spent 2 points in PW:S by then with the 3rd at level 31. So that works out to +15% or 1.65.

Level 32 gives me Flash Heal(3) 327-393 for 185 (1.77). Along with Renew(5) which will be 362 for 170 (2.13). That puts Flash Heal as my least efficient spell, with Renew in the middle and Heal(3) at the top of the list.

Skipping ahead to level 40. I'll have the following talent points: +15% Renew, +15% PW:S, and 10% less mana for insta-cast spells. I'll have the following spells at my disposal:

PW:S(6): 438 (381 base) for 225 (250 base) = 1.95
Renew(6): 460 (400 base) for 185 (205 base) = 2.24
Flash Heal(4): 400-478 for 215 = 1.86
Heal(3): 566-642 for 255 = 2.22
Heal(4): 712-804 for 305 = 2.33
Greater Heal(1): 899-1030 for 370 = 2.43

At least, I think that's how the values will work out. Looking at the values, I'll probably only use the following spells at 40:

Renew(6) 460 over 15 sec (2.24)
Flash Heal(4): 400-478 in 1.5 sec (1.86)
Heal(3): 566-642 in 3.0 sec (2.22)
Greater Heal(1): 899-1030 in 3.0 sec (2.43)
PW:S(6): 438 shield insta-cast (1.95)

While I'll be more likely to use Renew then Heal, it can be useful to have a decent efficiency slow heal that only does half of what Greater Heal does. That lets me be more efficient about topping up someone's health.