Howdy.

Do the horses from riften have more strength than the ones from windhelm.

i am thinking this as my windhelm horse died 4 second after buying it because it fell 2 yards.

my horse from riften is still alive along with vigilance (who ran into a bandit 'Area') and will fight for me and the bandits don't kill him.
do they have strngth differences.

Nope.

Unfortunately no. Only two horses in the game are more powerful than the generic ones. Frost and Shadowmere.