I tend to go through my seedlings on a more or less regular base. When I find something of interest I mark its label with red tape on the backside and turn around the tag to make the red marker clearly visible. As my seedlings are currently super crowded I usually do a transplant right after selection.
My usual criteria are colour and/or shape/surface structure. Size comes later. If there are several seedlings with similar shape/ colouring I obviously prefer the bigger/ healthier looking ones. Some seedlings are super slow growers in the first year. But make a growth spurt in the second.
That's why I prefer to go for size in the second place and look more for interesting traits in its appearance.
My only yellow seedling is a terribly slow grower, but still a keeper. Let's see what next year brings.
My only variegated seedling was a terribly slow grower in the first year and increased its diameter by more than 5times in the second year and grew into a beautiful rosette with 3 offsets, but completely lost its variegated colouring.
Another one I transplanted like 4 weeks ago was yellowish with a bright pink centre (that's why it got selected), now it has turned into an ugly dark greenish-brown.
You never know what you get...
