Tank suggestions

In the new year in going to have my 60Litre (13 ish gallon) available when I upgrade. It was my very first tank, that I learnt A LOT of lessons from years ago and it's long due a final makeover. It's bow fronted with the filter inbuilt into the back. I will be taking all of that out so there is more room and it will run a lot better.

My question is.. what has been your favorite animal to keep and why? I'm look for a species only, like axolotl (however i know this will be too small for one, sadly!) It will be going in my bedroom so something personable but suitable for a 60L