Trade in will give you less but should be quicker & less painful (dealer does the work)
Selling it outside will, 9 times out of 10, get you more $, but may take a while & may be a slight hassle dealing with idiots (DMV included).
If you go with trading it in, take off as many aftermarket items as you can because the dealer will just pull out his/her NADA book & tell yout the bike is worth $xxxx. They don't care that you have $xxxx into it. They'll just give you the book value, maybe a little more.
You can sell the aftermarket parts you took off to help make up some of the difference between book value & outside party value.
Provided you're not going to lose too much (only you know what is too much for you), trading it in isn't that bad of a deal.
Another factor is if you owe money on the bike.
If you owe money & your "upside-down" (owing more than the bike is worth) then that won't be good because that will make your payment higher than it really should be.
If you own it outright then you'll have to determine what you're willing to, realistically, accept for the bike.
I owned my last bike when i traded it in & took $1,500 less than I wanted because I new I could make up some $ selling some parts. That's just me though. Good luck to you.