i wouldnt go for the most popular ones.. because, it might take some, maybe a long time, before jagex gets involved and the owners & developers either get scared & shutdown or they get sued and forced to shutdown lol.
Take soulsplit.com for example. yea they ran pretty much #1 rsps for like 5 years r someshit but they recently shutdown.
it was like a year ago but Ikov shutdown for a little bit, idk if that was because of or had to do with jagex but yea.. its just a matter of time before they'll eventually shutdown for some reason or another.