I’m going to say avoid. Start on something smaller and sit on getting something bigger until you’re getting bored with something smaller. When the time comes, you’ll have no problem selling it to someone else for about what you paid for it.
I started riding a few months ago on a Ninja 250, and have yet to find a time where more power would come in handy, other than highway going squidly speeds. There’s never been a time where I had trouble merging in highway traffic or passing another car due to lack of so called power.
Having about 3000 miles under the belt, I’d be reluctant riding a 600cc sportsbike. There are guys who started off on 600s, and got better. But then there are those that didn’t do so well. Case in point, a class-mate in high school of my significant other. He was about to do a trick riding a CBR600, turned around to make sure everyone was watching, power got ahead of him, and before he knew it he was out of the student parking lot driveway, running into the side of a car on the street passing by the school. RIP.