I beleive that it would be best to stick to the 152 because,
1)It is cheaper
2)It is an easier less sluggesh a/c to fly.
3)You can convert anyway when you have your PPL
4)For the new pilot the 152 is ideal as the PA28 I find is much more hands on as it has mechanical flaps!
5)You will save much more money flying the 152!
Benefits of the PA28,
1)You can take your mates in the back and impress them/scare them.
2)It has a higher cruising speed than the 152.
3)There is much more leg room in a PA28 than a 152 i'm short but for tall people this would be a benefit.
4)The PA28 looks nicer, but that is never an issue when you are training
There you go i've rounded up a few benefits of both a/c!
Happy Flying!
Int.