Besides the wallet the truck that you have will be the limiting factor.
Know what your truck limits are & go from there. Hopefully what you really really want also happens to be well within truck specs.
In the new vs used decision I like the slightly pre enjoyed. Something that is a season or so old, had all of the bugs worked out of it & has been well taken care of. I also prefer to pay same money for a used top quality unit rather than a new mid market who knows what.
Last thing, try to buy your last rig first. Do the research, then do some more. The people who are turning over rigs every couple of years are people who have not done the research. They are paying for their mistakes bigtime. With some luck one of these mistakes is just what you want.