Hey Dusty, I think the twinkle is the best oncidium choice, not as big as the sharry baby which you'd be gobsmacked by how big it gets but not too small that it gets overlooked. They take up much less space than even a medium sized phalaenopsis, the flower spikes grow up and don't take up any more space than the pot below. They are very adaptable too but if you are looking for something smaller then you should certainly consider its parent the oncidium cheirophorum which is the smaller parent of the twinkle so stays very compact.
The cheirophorum is a hot grower however so not as versatile as the twinkle.

Something that stays a similar size as the cheirophorum is a mexicoa ghiesbreghtiana, a warm to cool grower but if you truly want a mini oncidium then a good candidate might be an oncidium coloratum.

Dont be fooled by descriptive words when looking for them. I know a grower in the UK who has a Twinkle that has 'Tiny' in the name and that plant is a lot bigger than any of his other named Twinkles.
I've never come across come here, maybe its just sold in the UK.
I've added a link to the video. He shows a couple of mountedTwinkles first, then at about 11 minutes in he shows the Tiny Twinkle.

My Sunday Orchid Chat - A Quick Look at My Mounted Orchids - Yes, ALL of Them - YouTube

Nice video link Diane! Quite relaxing to watch, and saw the Tiny Twinkle at the 11 min mark!

Thank you. I will add these to the list for later.

Jumping on the twinkle bandwagon, I love these little guys! Here's my 'pink profusion' still getting ready to bloom.

https://i.postimg.cc/fR3NmbKk/20210830-201257.jpg

I haven't seen many Twinkles that big. You can divide them to keep them in small pots. They flower with only 2-3 pseudobulbs. I have seen plants flowering in 2" / 5cm pots. Of course the show is better with a bigger plant.

For a mini Onc., consider what is usually sold as Howeara Lava Burst. Its ancestors have had name changes, so it is now supposed to be called Leomesezia Lava Burst.