Poison was my favourite till i acquired bladestorm. Always used that for paladins and also for arblasters when I was a midlevel player. All towers have poison resistance so that is not much useful at higher levels but I feel like Ogre seem to be having some hidden weakenss to pioson too. Some time mortors are having a good effect on ogres but nothing like arblasters to counter them.
Swordrain especially and Hammerstrike are making a come back. I guess you need to be atleast 80 + king for that. After I max my heal spell, I will concentrate on sword rain. Sheild and Blizzard are the only spells that are still at level 2 for me. I never saw a single attack with shield till now. I atleast saw very few using blizzard now and then.
@Killemog visits me often with Hammerstrike and is quite successful. So yes you play with what you are comfortable. As for as monsters, I am having more success with Ogre-4 than mummy-3 in attack and I havent come accross anyone using Ogre for attack on me yet. So I guess it depends on each persons style as to what you use.