I am a great fan of mixing up aircraft types.
BUT
I have just had a stroll through my log book and, to my surprise, all my PPL training was on C150 - 12 hours, followed by a 15 year break, then 49 hours over a 12 month period to PPL. So from a student point of view I am with Mr BPF.
Since then I have jumped at every opportunity to try whatever is available - 10 disparate varieties so far. This has (in my view) improved my handling and my adaptability. While the PA28 does have many things to recommend it, from my not-very-experienced point of view there is more airborne pleasure to be had with other machinery when it is available.
SD