I've cruised NCL 'solo' three times - in the past eighteen months.
Cabin 1 - Aft Balcony, due to some upgrades and booking issues
Cabin 2 - Standard Balcony, having bid on a upgrade from a inside - the inside was the same price as the Studio
Cabin 3 - Studio - Which was my first cruise out of about 9 where I didn't have a Balcony.
I don't tend to do much more than sleep / shower in my cabin when cruising solo, so found the Studio perfect. The modern decor, mood lighting and 'studio vibe' was nice and the layout worked well. I'm 6ft and average build but could see why some might find it a bit tight.
I tend to go to the Solo meet (which anyone can go to) to put some face to names, I've never spent any time in the Studio lounge at solo dinners or shows. I found I made plentry of friends on the ship that I could drink and on occasion have dinner with but also my time.
That's more around solo experience - having never done a inside, I think I'd book a Studio over a inside if price was equal - but thats more I liked the modern feel of the room and how functional it all was.