Get one with an Intel i7 or i9 processor. After that, as much RAM; as big a disk; as large a screen as you can afford. Pick a known make such as ASUS or HP, keep away from IBM or 'Lenovo' as they are now called - they have a bad reputation currently according to 2 of my sons who work in the business. You might try
www.pcspecialist.co.uk where you can specify a machine built to your desire. Or, check Amazon outlet - they sometimes have super deals on - I bout a £1700 Asus machine for £1k via that route - brand new/unused, perfect, with full warranty but unboxed. Whatever you do, DON'T buy from PCWorld or similar!!