I have a well set up 2011 250 with KYB suspension and a 18 250. In my opinion it's not even close. The 18 is light years better. I hate to say it but I like it more than my Beta 300 also.
I own a 13 Beta 300 and my wife has a 18 ec 250. I rode a 18 tx300 last year more than enough to know that the only thing it has over the Beta or the Gasser is the counter balancer.
It's an EC and we also have an 11 EC250. Engine power and character is very similar between the 11 and 18 with the 18 having way less vibration. Think of it as a more refined.
I have a Beta 300 and a new GasGas 250. I like the Gasser better but it is a bit wider. Hardly noticeable unless you have the bikes side by side. I'm not sure if anyone else has this problem but when making deep left turns with my leg out somehow I tend to hit my knee/inner leg on the Beta this...
I own an 18 ec250 and spent as much time as I care to on a 18 TX 300 and in my opinion the GasGas motor is very low on vibration but still not like a KTM/Husky motor. But the GasGas is a much better bike overall out of the box.