In a Monitor. I thought I remembered your name from the issues with the water a few weeks ago. I am sorry that it died on you. that said I was wondering why you would go from a water to a nile. As someone who works with waters and has had niles I found that odd. While both species can be aggressive captives niles are a bit more defensive and nervous than waters although they are smaller in size (weight wise they are similar in how long they can get.).
I googled some of your past posts here on kingsnake to see what makes you tick so to speak and to gage what kind of experience you have with reptiles.
Although they were from 2 years ago and people can learn a lot and gain much experience in 2 years I found your questions on venomous snakes and anacondas to be a bit spooky but typical of someone with not-so-much experience with reptiles. I do not mean that to be insulting (all of us were inexperienced at what we do at some point and no one knows everything about all animals.) and with that said I commend you on asking for advice before jumping into to something reptile wise that could be over your head .
some of your older posts in reference to falling asleep on the couch while handling reptiles concern me and make me wonder what you are looking for in a monitor. Monitors are not lap dogs if that is what you are looking for you should get a cat or a dog. Niles and waters get large very quickly and require enclosures the size of small rooms and while having a pool with them is not necessary being that both animals occupy a riparian habitat they do much better with a pool and certainly exhibit more of their potential behaviors. You should take these points into consideration before you purchase an animal you may not want or be able to handle down the road. I am certainly not trying to discourage you but trying to make sure you know what you are getting into before you do. with the right research you may find one of the smaller captive bred species more suitable.