Sleep, without a doubt. Spontaneity. Having conversations which are not constantly interrupted to say 'stop that' 'shush please' 'in a minute' to a small person. Freedom. Not needing to pack half the house to go out. A few months ago I would have said evenings too, but we've since cracked bedtime.
However, it does get better dd was 2.5 when ds was born and we were finding life getting easier and easier in terms of sleep, eating out, how much pariphinelia was needed.
Dh and I take it in turns to have lie ins (much needed with ds the sleep thief), to take dd to dance or swimming etc so it's not all on one person.
I've also gained a lot, a new respect and passion for my job as I felt I lost my identity on mat leave a bit. Some great friends I met in a parent and baby class who I still see regularly with and without the kids almost 4 years on. And two children who my god I need a break from at times, but who I look forward to getting back to at the end of the day.
Oh, and I would say I'm more carefree in some ways (worrying about the children aside). I remember cringing as a kid when my mum would chat away to random strangers in supermarkets, I am now that woman. I think in general I give slightly less of a fuck about stuff outside my home life.