We got a terrier cross (Jack Russell cross yorkie) as a first dog.
Pros
Very clever, housetraining was easy, he picked up all the command's really quickly, we're now doing agility with him.
Extremely loyal and faithful companion, he loves us with absolute devotion.
He's around 7.5kg so easily portable, doesn't take up too much space and doesn't eat much.
Other than the odd bath and brush and a yearly hair cut there's very little grooming needs.
He's fab with people he knows, kids and lives happily with our cat.
Can take him anywhere, as long as he is with us he's happy.
He's a sturdy and robust dog, he is up for anything and loves a good adventure.
No separation anxiety, he just takes himself off to bed when left at home.
Cons
He can be a bit nervous of new people (is fine once he's decided they're okay!)
He isn't great with other dogs especially other boys. We have worked really hard at getting him to ignore other dogs and 99% of the time he is fine now but I still can't completely trust him around dogs he doesn't know.
He can be a bit barky in the garden especially if he sees a pigeon!
So all in all the pros massively outweigh the cons, we have put a lot of effort into socialisation and training but I think that's the case with all dogs tbh.