buy the bike that you like - take a good look in person, sit on it, ride it (like you did) and choose carefully
MT25 and Z650 are very mature platforms, so both should not go wrong
many ppl go out search bike, and find the one that love at first sight
some ppl did research, bought a bike, and regret
depends which type person u are
engine CC is a small factor in deciding what you buy
250cc is overstressed for high performance given the components that is used
the 650cc is built to last and the this year model is bike of the year for some people back then -
https://www.motorcycledaily.com/2017/12/md-...-and-ninja-650/given your experience, the 650cc will be more suitable as workhorse
but, it's underpowered compared to peers - this may mean better reliability and more suitable for riding into areas with lower quality fuel
also, the 650 engine has different vibration character, diff bikes vibrate at diff RPM even for the same model. Some don't vibrate at all because the vibration range is spread out evenly. this is something u cannot fix.
maintenance wise, some ppl live with no fuss for both models, but some ppl kena issues like F1 team sponsor. YMMV, which is why I say the most important is getting the bike that you like and be able to fix it along the way. you can't have patience for something you don't like
but, of course, I hope no one gets into bad situation with a bike they get
in my case, I kena few issues - some that is common, some no one even heard before
First thing to do:
- voltmeter - charging voltage and cranking smoothness can show battery condition, do not hesitate to change a battery. It is more expensive to change stator coil and rectifier.
- do not cheap on oil and maintenance - good oil cools parts more effectively, especially valves along the way. A cooler valve elongate faster than a hotter valve, so think valve clearance, top end hancur, and cost of disaster. Oil is not just for lubrication.
- do not pressure wash the bike, only splash wash, mild brush, and rinse.