Best computer you can buy is always a custom built desktop. For $1500 you can get a pretty nice system, but it seems like you are more interested on a laptop. Games like counter strike and runescape are not very difficult to run, so most any computer can run them fluidly. So now it is up to you to decide which one you want
Custom building your own pc is definately the best option with your budget. Although you don't seem too interested in playing high detailed games @ maxed fps, so you shouldn't even consider it. Although if you are planning ahead, a custom built pc may be the way to go, you know exactly what is inside it, which is always a bonus, and they normally last quite a bit longer than laptops, due to the fact they aren't as easy to overheat as most laptops. Nevertheless, good luck with your decision
I was thinking about replacing my pc completely aswell with a laptop. And maybe keep my monitor, mouse, keyboard, speakers etc and use a docking station
I would definitely get a desktop. You can get a desktop with the same speed and ability for half the price of a laptop, and with 1500 dollars you can get a pretty damn nice one. This is if you're planning on only gaming at your house. I would recommend getting a cheaper laptop for whenever you need a computer, and you aren't at your house.
Not sure if you read his last reply, he said he's ending gaming in his life, apart from basic low fps games such as counter strike, and runescape. I have no experience in custom building laptops, i doub't it would be too hard and you could ask around for some help. Macs are extremely overpriced in my opinion, but im a desktop man, so don't take my comment to heart. Good luck.
Honestly, you think you'd use a laptop a lot and on the go until you own one. Mine just sat as a pseudo desktop for 4 years till I built one.