Well, I can only speak for myself... For me Z-scale (1:220) is no alternative due to its tinyness, and my deteriorating eyesight and general clumsiness when it comes to small parts does not make it an option for me... Z-scale is cute, but also lacks details... In N-scale (1:160), which I had for a while, you have working full working valve gear and such on steam locos that you don't get in Z... If I would do Z-scale, it would be of modern prototype as ICE + electric and diesel, and not steamers which are my favorites in model railroading. The H0 scale is very good detailing-wise but is a bit space-consuming indeed. My personal preference would actually be something inbetween H0 an N-scale. There is such a scale called TT (1:120) but unfortunately it is not as widespread as it deserves to be... So for me it will have to be H0 at the moment...

If you have both scales now, why not just do both, but only expand one in the future. Maybe do a small Z layout with the equipment you have, but leave it at that. Build the HO layout too, but only buy new stuff for HO in the future. That way you can enjoy both, but expand one scale in the future to grow in the hobby. I personally like a lot of scales...each has their own advantages. Z is certainly a great one that is growing here in the U.S. Marklin HO has more stiff competition in the U.S. from two-rail DC HO, so it is not as widespread.

My Kato N scale locomotive ran like a dream...but I was forced to clean the track daily -- and sometimes a few times a day if I ran trains a lot due to the build-up. Thus ended my N scale experience due to the frustration of the constant maintenance on track cleaning. You are so right -- Marklin HO is a "breath of fresh air" in terms of operating...and I wish more people here in the U.S. would give it a try...they just might love it! I do have clean my C track about once per week -- but nothing like what I did in N scale.