I'm working on a particularly tough level and I only get to choose a few Defenses. For a long long hallway, do Floor Spikes do more damage to the Heroes than Wall Blades?
Since wall spikes are invincible and can not be disarmed by thieves I'd say that they are the better choice.
You can however protect floor spikes by putting a defence (preferably wall blades or wall crusher, which can not be disarmed or destroyed) just before them, so whenever a thief tries to disarm the spikes he will get hit and stop disarming. As an added bonus, depending on what defence you put there, they will also be pushed back and have to pass your trap once more.
Also note that if you cover floor spikes thieves can not disarm them.