Which is safer? The Piper Tomahawk or the Cessna 152?
From the Wikipedia article on the Tomahawk:


  Safety record:
  According to the Aircraft Owners and Pilots Association Air Safety Foundation, which published a Safety Highlight report on the Piper Tomahawk, the Piper Tomahawk has a one-third lower accident rate per flying hour than the comparable Cessna 150/152 series of two-place benchmark trainers. The Tomahawk has a higher rate of fatal spin accidents per flying hour. The National Transportation Safety Board (NTSB) estimated that the Tomahawk's stall/spin accident rate was three to five times that of the Cessna 150/152.[2]


Earlier in the article it was stated:


  Before designing the aircraft, Piper widely surveyed flight instructors for their input into the design. Instructors requested a more spinnable aircraft for training purposes, since other two-place trainers such as the Cessna 150 and 152 were designed to spontaneously fly out of a spin. The Tomahawk's NASA[1] GA(W)-1 Whitcomb airfoil addresses this requirement by making specific pilot input necessary in recovering from spins, thus allowing pilots to develop proficiency in dealing with spin recovery.


So what this means is that the Tomahawk was intentionally designed to be easy to spin so that instructors could teach students how to recover from a spin.  Other aircraft, like the Piper Cherokee, are almost impossible to spin so instructors cannot really teach spin recovery in those aircraft.  

To answer your question on how this relates to safety that depends on how you look at it.  I would argue that a pilot who knows how to recover from a spin is a safer pilot than one who doesn't.  However since the Tomahawk is actually made to spin, there is the potential for increased spin/stall accidents if the pilot messes up.  Aircraft like the Cessna 152 or Piper Cherokee have design features that can "cover up" a pilots mistakes because they are difficult to spin or stall, but if you plan on flying aircraft that are not so hard to stall then not knowing the proper recovery procedures can get you killed.  

The main factor in safety is not usually the safety of the plane but the safety of the pilot.  The vast majority of accidents are caused by pilot error.  I would worry more about evaluating yourself as a pilot and understanding if you have the right mindset to be a safe pilot.