John,
I presume the representative from the aircraft company had a product he thought was superior to the 150/152??
I did my instrument training in a 172. It's a nice stable platform - and a Cherokee would be about as stable. There's no doubt that these are more stable for instrument training than a 150/152, but the little one can be used. You will have to make some adjustments - they are more bouncy than a 4 seater. On the other hand, we can get slower, so there's more time after you hit the IAF to get it all lined up before you get to the runway.
There's good arguments for just about any plane for your training. If you're going to be flying a 150/152 IFR, then go ahead and learn how.
Ed
