Hiking on TM is mostly safe if you have good mountain sense and are prepared. Having said that it is always advisable to take a knowledgeable guide. This is so much more of an experience than just walking you to the top by the shortest possible route with lots of other people.
Active Africa uses the best guides for a great experience.
Otherwise Vertigo Adventures or Hike Table Mountain are good service providers.
I have worked for all three and can recommend the experience.
Shout if you need more info.
