question, do you intend on upgrading for bigger bike in the future?
if you do, take the 250 instead. Its cheap as fuk and if you drop it, you wont cry.
the 250R is good bike for learner like you. I assume you are going to daily it? 250 fits the requirement.
Reason Im saying this, the 250R basically has the liter bike appearance for the quarter of the engine size thus it'll teach you how to ride the bike.
my pov, 650R wont last you long. You WILL want to go bigger. So, rather than spending money on the 650, why not just be cheap for a while and get 250 instead. From there, learn the 250 to its fullest. Its not about the size, its about the skill of the rider. A damn good 250 rider can gives the big bikers a good run for their money. On twisties that is.
when you are done with 250, then you can go straight to liter bikes. Wont be a problem.
ask
kapalterbang_737, he owned 2 Blade 250R, one Ninja 250 and now he rides an 06 R1..
one thing is, our human brain is brilliant. If you jump to 650 from 125 and starts riding, your brain will kick in the
'dont drop the bike' mode. And its gonna take time to get use to the bike. Furthermore, its also related to money. If you drop it, you gonna spend more. Thus, dropping the bike really is not an option.
while the 250 on the other hand, your brain will be in the same mode but, its less stressing to you. The throttle is less responsive than the 650, the torque is also forgiving for newbie thus, you will tend to push the bike more. This will make you experience more and learn more of the bike behavior.
there, Ive shared my little tiny bit of knowledge. Its up to you to decide.

regards,
keyboard warrior.