Personally, I wouldn't go for a laptop if you can help it. Desktops will allow for much easier upgrading and overall will be worth more for the money you pay.
If laptops are your only option, then I suggest you make sure it had a very good battery, its own independent graphics card and at least an i5 processor or any of the new AMD Ryzen chips. Around 8GB+ RAM and an SSD for faster data transport overall. I'd imagine that would be in the region of about £500-£700 [$700-$900]