Another vote for a yorkie.
I've had lots of dogs and used to be a dog walker/pet carer, including looking after loads of puppies for people (I loved that).
Some breeds smell more than others
Some dogs are super chewy when puppies
Dogs that aren't particularly smelly still smell gross when wet except for non shedding dogs.
House training takes time - some dogs harder than others
The thing is, the downsides vary depending upon the breed. I live with three different breeds at the moment and they all have their downsides.
Back to the yorkie, so I got a yorkie and like a PP said, best thing ever. That's not to say it's been easy. It's not. She's a special needs dog who is completely blind (eyeless - removed) and that has brought its own challenges. This was unexpected and is down to bad breeding. It has cost me a lot to deal with in vet/hospital fees. It's all stable now.
As an example of this breed...
Positives:
I think of her more like a 'catdog'.
Her size means she is more cat like in expressing love, so sitting on your lap, squashed next to you on the sofa or in your arms having a cuddle
She travels very well (never once sick or messed in the car)
Doesn't need masses of walks & happy with just playing to expend energy as well
Fine being left for a few hours (curls up and goes to sleep) and if going to a friend's is the kind of dog you can bring along and no one minds
Doesn't shed/single layer coat (no hairs on your clothes, furniture, floor! - amazing compared to our previous dogs that heavily shed)
Doesn't smell - thank goodness as I do not like that dog smell
Never chewed or destroyed, but I gave her loads of chews and toys as a pup/young dog
Great recall - has never run up to another dog or a person as prefers me and comes straight to me when called
Children love her and she loves them - if I take her in Pets at Home I get mobbed by little children wanting to pet her. She was brought up, until I got her, with 3 children under 12 and so is great with children
Downsides are:
Teeth need cleaning well as they are tiny and if that doesn't work you have to pay for dentals (done under general anaesthetic)
Can be fussy eaters
Terriers are quite willful
Needs bathing every 1-2 weeks
Need either clipping short or daily grooming as the coat will grow long
Can be quite dependent (but then so is our rescue lurcher!)
Small size means little children need to be very respectful of these type of dogs
Not the kind of dog that would be good left in kennels - better left with a relative or one of those in-home boarding services (your dog stays with a person in their home)
House training was hard in comparison to bigger dogs I have owned or worked with