I had some fun with Z & N, but the delicate nature just wasn't suitible for the then very active household. Floor vibrations would cause a derail in both, & HO, well, way better, but really no smaller than PW- O when you look at the dia....and Tyco had left a bad taste I'm trying to shake to this day.
I have a lot of respect, esp. for the track laying abilities, of Z modelers. I have the skill (novice, lol); just don't have the patience anymore. My first repair and led job was satisfying and I'm glad I tackled them, but that was the cincher too; O was just too easy.
Prototypical operation is low on my priority list and a move to less space inevitable, so I've experimented with small engines and building micro loops in O (thanks Ace) and found them lacking in run appeal slightly, but very fun none the less. Maybe more fun to build. Faster for sure, and when done, there is still room for the next one to be started. I have three with less footprint than the 4.5x9.
If you have no Z experience, I'd dip a toe and swim some before diving. They ARE fun, but they are not O. Running them a while is the only way to know if you need a name change 
More specifically, backing up. The straight between curves to avoid an S at all costs in now pretty much gospel. In O the warning is a joke compared to small scale.
