+SPD/-RES Soren?

uhhhh,
Soren with (Res) as his bane is at 26 resist and he'll have 36 speed on a boon...
This doesn't make sense to your comment as
a normal Nino is at 26 resist and has 36 speed... so he'll be no better her (Unless) she has a bane in res or speed... and soren only has 3 more life so that odds are Nino is better 80% of the time I'd say.

With this said units that are naturally better are Anna and Titania for speed&res for tanking. Anna additionally has a naturally larger hp pool.

Fae seems to be decent as well though for green taking there should be better units.

36 33 36 17 26 Soren +Speed -Res
33 33 36 19 26 Nino
(all it takes is a nino with a boon in res or speed to tank better than your current soren.)

Non-Mages
46 33 28 25 30 Fae
not the most tanky but decent and recover helps for your needs. though I assumed you wanted fast units due to you choosing Soren before
41 29 38 22 28 Anna
Higher life, res, speed, basically better for your needs but she is melee.
37 28 34 25 30 Titania
Covers the same distance, and with a boon speed is just purely better than Soren for what you said.
Sadly she is melee so she may not fit you role.

Unfortunately, those IVs basically turn him into neutral Nino with 3 more HP and 2 less DEF. If you're looking for a Green Mage wall, I'd either hold onto him to merge with a better Soren down the road or use him for skill inheritance fodder.