Which is safer? The Piper Tomahawk or the Cessna 152? I have booked my first flying lesson for 2 weeks time, in my first step to obtain a PPL or LAPL. I had done all of my research on the Cessna family, assuming that is what I would learn in. I was satisfied by the safety and glowing reviews by students and instructors alike.
Anyway, my local school has since told me that they don't have the 152 anymore, so I will be learning in a Piper Tomahawk. Some quick reading here states:

The PA38 accident rate ranged from 0.336 to 0.751 fatal stall/spin accidents per 100,000 flight hours, compared to 0.098 to 0.134 for the 150/152.

and

There was always a concern about the stall and spin characteristics of the Tomahawk. The old adage “be careful what you wish for” applies because an overwhelming majority of the PA38 survey respondents requested an aircraft that would stall with more authority than the 152. And they got it.
You’ll hear many people talk about the stall characteristics of the PA38 like they’re referring to a demon, but it should be remembered that this was essentially a design feature to teach better pilots. Unfortunately, this led to a higher than average stall/spin accident rate that earned the PA38 a less than admirable reputation quite quickly (thus the nickname Traumahawk and Terrorhawk).

This isn't as comforting. So taking into account engine reliability, stall issues, etc. - which aircraft really is safer?
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.