Do yourself a favour and go to a well reputed bike dealer and sit on a few. You don't even need to ride them at first, it's just to give you an idea of the feel of the various types of bikes. There are billions of Youtube videos about beginner bikes and everyone's got their own take on this topic so whilst it might be good to get some ideas, at the end of the day what suits you might not suit someone else. It also depends on your usage profile, a supersports as a commuter will kill your back in a week, whereas a little 125 for Sunday rides will put you off riding fairly quickly.
Personally I'd be staying away from litre bikes until you've built up some confidence. Yes you can get on them and behave yourself, but all it takes is one moment of weakness and you're either without a licence or being stitched back together in hospital.
As for actual recommendations, my recommendations would be Suzuki SV650 (cost buttons used, everyone knows how to fix them, parts are everywhere, easy to ride and still great fun), a Rebel 500 (very comfy, not the fastest bike in the world but will give you millions of miles of worry-free riding and low maintenance costs), for something sporty you could look at a CBR650R, which looks a bit sporty but is still a rather decent beginner bike. Another option is a CBR500X which has more of the off-road / adventure bike look and is also fun to ride.
You'll likely be doing your test on a 500-600cc bike, however it'll be restricted so whilst you can gain a bit of appreciation for the chassis / comfort, don't think that the power you're experiencing is what you'd get on an unrestricted bike.
A huge factor with bikes is being able to stretch their legs. I've said this time and time again, it's a lot more fun to ride a slow bike fast, than a fast bike slow. An R1 is nice and fast and all but if you value your licence you'll spend most of your time in second gear, whereas something like a CBR300R you can ride the absolute nuts off and still be relatively legal and also a lot easier to scrape off the road should you have a spill. You only fall once on a litre bike.
