Welcome to the site !!
Pretty much agree with Neil , its kind of a "how you feel" situation , What you did not mention was your Weight , actual Skill Level , and Age and goal , are you planning on racing ? , are you planning on trail and fun riding and occasionally going to the track to ride with your buddies ?? , do you plan on hitting the track every weekend but only for "practice" ??? , with no racing in the plans ???? , those things make a difference as well , .... If you like the smoothness of the 450 , will you like it after a hour or more of riding hard and your arms feel like they are being torn off ??? , because a 450 WILL wear you out faster no matter how "easy" you ride it , a 450 will wear you out due to the power/torque , but with a 250 you will have to rev the crap out of to get the performance out of it that you have at your fingertips with the 450 , but at full power it will feel like a 450 in 3rd gear , and you will be going "is that it ??" , but at the end of a couple hour ride , you will be much less tired than after the same time on a 450 , a 250 favors lighter riders best , but you can do the suspension for any size/skill rider , but if you weigh 220 , your going to struggle with having enough power compared to your buddies flying by you on their 450's that weigh the same , with that said if your 130 and riding a 450 , its going to be the "my arms are being torn off" scenario
A 450 favors middle aged Vet riders (30's-50's) or young kids with no fear , it has enough power when you want it ,but you don't have to use all of it to keep the pace and have fun , where a 250 you have to ride it more like a 2 stroke , and keep it on the pipe and revving to clear the jump out of the corner , or to try to keep up on the straights , you can grow into a 450 , a 250 is what it is , and once your skill or power needs grow , the 250 is done and you will need a 450 , as a 250 is just a 250 , you can only get so much power out of it before it becomes unreliable , the average rider will never ride a 450 and say "i really need more power" , and if you add more power to it , it becomes unrideable
So hopefully you are not more confused as to what to get , but hopefully we made you think about what it is your looking to achieve , and gave you some guidance
You might also like to try a 350 , though Honda does not make one , nor do any of the other Japanese manufacturers , it would give you the best of both worlds , though the weight is close to that of a 450 , it allows smaller riders plenty of power , but you can ride longer like on a 250 but have more fun as your experience broadens , so you ride it like a 250 , but can grow into it and still have over 50hp at your fingertips and still have fun and you won't really outgrow it like you might on a 250 ..... food for thought....