Depends on activity level of your household, amount of time and money you want to spend on grooming, how much exercise you are willing to give it, if there are other pets in your household, if you are in an apartment etc.

Lhasa apsos and shih tsus are great small dogs but need to be brushed daily. Low exercise demands. They can be prone to alert barking when they hear noise. Won't be good dogs if you like to hike/walk long distances.

Cockers can be good, but can have high grooming demands, but can easily do longer walks.

Terrier breeds and schnauzers can be good, like jack Russell terriers, but can be barky and terriers can have more prey drive issues with kittens/rabbits, etc.

Pomeranians can have high grooming requirements and be yappy. Higher energy.

Havanese are great dogs but can be higher energy than shih tsus or lhasas.

Your local shelter may have the perfect small dog. Mixed breed dogs often end up being great dogs. Anecdotally all of my mixed breed dogs have lived really long lives and been very healthy. Many of my purebred dogs ended up dying younger from things like congestive heart failure, or had allergies. I think many purebred dogs are so inbred that it has affected their health.