both are great quads!
i like the z400 as an all around better quad but thats just me. so lets here what every 1 else thinks

 

never rode a 400ex, but I personally do not like honda, and all my riding buddies have reliability issues with their hondas, I love my suzuki, i think its just a great atv, all around, nothing I dont like about it, not sure which one was around longer though. The Z400 is probably more around as they have Kawasaki, Suzuki, and Arctic Cat being the same atvs.

 

suzuki all the way. the 400ex is and will always be a great quad, It was designed after the 250R that honda had, ive riden both and still I would rather ride a suzuki

 

Having owned a 2001 400ex & now currently a '03 Z-400, I'd say it really depends on your riding syle. They Z400 certainly has more snap once mild mods are done to it. However, when I had my 400ex I had an FMF pipe on it, of course jetting too, no airbox lid & a 14T front sprocket and was very snappy. The 400ex isn't a slouch, it just has a more linear powerband making it feel much slower. Ride quality is about the same, maybe the 400ex slightly plusher. Reliabilty is equal.

If I could find a nice, not beaten 400ex for less than $2000 I'd probably buy it. I really liked my 400ex, but really like my Z now too.