Best Of

I see the Shield Training has his spec layout at 5/5/3 as many have stated could be ideal. With so many web tiles created from SM99 & Gwen that should ensure great additional target damage every other turn or much more. 

Alternatively, I think there's some interesting math that suggests you could get more overall damage (throughout the match) with his black at level 5. Check out the assumptions below when set at 5/3/5 instead:
 
Black at level 3:  1262 damage and you get 3 of 3 CD's to resolve for 2309 each =   8,189 
Black at level 5:  1623 damage and you get 4 of 5 CD's to resolve for 3427 each = 15,331  (could get +3,427 if all 5)
     A difference of: 7,142  (and it could be 10,569 if all 5 CD's resolve)

Difference in damage from his yellow passive on blue and black (and yellow) matches: 
Yellow at level 3:  blue, black 380 damage each
Yellow at level 5:  blue, black, yellow, 633 damage each
     A difference of: well this is difficult, but: 2/7 of all matches results in 380 vs. 3/7 of all matches results in 633*

So for simplicity say we are 'giving up' 400 damage on the difference of an average blue, black, yellow match, it would still take 17 of these matches to realize the difference on the setting of his black (7,142 / 400 = 17.86) 

{If you happen to get all 5 CD's to resolve, the difference would be 26.4x of these web damage matches!}

And lastly, suppose you have his blue played at level 5, and that stunned enemy is taking 75% additional damage. On any of these CD's resolving, that too would be multiplied to a much higher total (it's random though).

Whelp, there went my coffee break.

*Passive Yellow set at level 5 means more web tiles created on yellow matches for even more web matches to follow, and most players will be actively avoiding TU matches if possible