any EX250 experts round here?

Yes, i know it's not a mainstream model round here, but since bottom end is essentially same as an aircooled 250's, let's give it a try.

Tempted to get a liquid cooled EX 250 for my girlfriend. Thing is that they seem to be less reliable than aircooled KZ250's or i am totally wrong? Case in hand, went to see one and it had a pretty bad knock with only 30K on the clock.... Only info i found on the net is just one guy who sounds quite inexperienced and claims that these motor just dont go past 30-40K without trouble. (no need to quote him again guys )

Would get a KZ250 but prices are starting to get silly here in Italy due to cafe craze while EX's are still cheap.
your feedback is welcome

Caveat: My wife owns one, but I am no expert.

I've not ever heard of a weakness in the bottom end, but it is pretty rare to see one in the US with that many miles. Nearly all of them here are bought by beginners who ride them for a few hundred miles an put them aside when they move up. It's not uncommon to find one that is ten or more years old with less than 10,000 miles on it.
There may be a member or two here with some expertise, though you might have better luck here. www.250r.net/

I don't know much about the Ninja 250, but I would get one in very good condition w low miles.
A bad voltage regulator connection might be typical as it seems to be a problem on the EX500.
The fix is easy --- just clean up the connectors & make sure they're tight.

faq.ninja250.org/wiki/Main_Page

tnxs guys, tried combing those places but maybe because it's mostly young guys on their firsts rides, very little on longevity issues,

many "no spark" or "bike wont run" threads though

oh well...

I have one, and they are pretty indestructible. You will need to be good with carbs however. My KZ 1000 has run with amazingly dirty, unbalanced carbs without a hiccup. The ninja 250 has very, very finicky carbs that need to be scrupulously clean.
That said, mine is running a big ass K&N filter, race jetting, and a SS pipe and sorry exaust I welded up. It sounds like a two stroke and accelerates like nothing else. So long as you remember you will never break out of double digits, EVER! Very fun to mess with and customize. Parts are insanely cheap too.