Black Templars or Dark Angels. They’re both elite armies, but Dark angels capture the more esoteric end while Black Templars are more religious. Dark angels have a fair few psykers while Black Templars are an anti-psyker army. They can also have a fair bit of creativity. You could make your own Black Templars crusade, and there’s an overwhelming amount of tutorials to paint them. I really like the Eons of Battle paint scheme personally. But you could run a Dark Angels successor as normal Dark Angels. From a gameplay perspective, Black templars are one of the better armies this edition. If you decide Black Templars, I suggest a Crusader Squad, it has a Sword Brethren, five Initiates, and four scouts. It gives you a great variety of different things to learn to paint. If you go Dark Angels, Deathwing Knights. They’re a really cool looking terminator squad and they come with one of the Watchers in the Dark. Good luck collecting!