I am not yet really familiar with the fifth edition, but as far as I know, it seems important to me to also consider that +2 WIS is also a boost to your save and some skills which can drastically affect your survavibility.
Instead of giving you my very own answer which may not be your depending your style of play, I will give you list of pros for each option.
Pros to +2 Wis
- +1 to perception checks means that you will less likely be surprised by a sneaky character, which makes quite a difference for a squishy character.
- +1 to save is always good to take even more at low levels... Yet it is a weak save for you, so at lvl 20 I doubt it will make a huge difference.
- +1 AC is pretty good, it ends up as a 5% miss chance which, on the long run, is better. Well, before lvl 20, enemies tend to hit significantly harder than 20 pesky damages. It won't do much better than "buffering", at best, a single attack.
Pro to +2 Con
It gives you +20 HP so about 21 % more HP. It is a good bonus to your survivability yet it won't save you from a bruiser's beating.
CON 12: 8 (monk) + 3.5 * 19 (average sorcerer HP roll) +20 (Con) = 94
CON 14: 8 (monk) + 3.5 * 19 (average sorcerer HP roll) +40 (Con) = 114
+1 to one of your strong saves, which is good and probably better on the long run, as the system seems to encourage you to be good in your area of expertise and count on friends to compensate your weaknesses.
As told previously, +1 CON won't net you the best result in term of sheer HP bonus, if you are really looking for a boost, for your HP, the feat 'Tough' is a better alternative.