This is tricky. I'd say do it for non-martial classes. For martial classes, you'd be surprised, some monsters are better than if not as good as characters of the same level... lemme give you my list:
My criteria is this - will I have more than or equivalent hitpoints to a fighter of the same level? Will my attack after str mod be better than or equivalent to a fighter of the same level.
The way I've phrased these is how many class levels the monster needs to take before it is equivalent to a fighter of the same level, and how many total it needs to be better than a fighter of the same level.
Blackscale lizardfollk: viable after 4 levels, better after 6.
Erinyes: Viable to start off with, better after 1 level.
Bralani Eladrin: Viable after 5 levels, better after 6.
Troll: Better to start off with.
Gargoyle: viable after 4 levels, better after 5.
Gargoyle advanced to large (7hd): Better to start with.
Stone Giant: Better to start with
Gnoll: Viable after 3 levels, better after 5.
Lizardfolk: Viable after 3 levels, better after 5.
Hobgoblin: Viable after 4 levels, better after 6.
Minotaur: Viable after 2 levels, better after 4.
Ogre: Viable after 2 levels, better after 4.
Sahuagin: Viable after 8 levels, better after 12. Special consideration for the 4-armed.
Half-Celestial: Viable after 11 levels, better after 12.
Half-Dragon: Viable after 8 levels, better after 12.