Best to put them in the ground now, where you want them, there's no advantage in growing in pots over winter. The risk is, if they're growing in pots next year, you might damage the roots when transplanting, and unless they're some type of hot house alliums, they do need to be outdoors, in a pot or in the ground, and if we get a harsh winter, there's a risk the pots might freeze, which would destroy the bulbs.

If you're a bit worried you might not remember quite where they are, put in a pea stick or two after planting to remind you.

The only time I'd recommend growing (and keeping) them in a pot is if they are Allium triquetrum, in an attempt to prevent them taking over the entire garden.

cheers

I had also intended to pot up some large alliums and plant out when I could see the growth from the existing alliums starting to grow. Last year I ordered a mix of white (mount Everest) and purple sensation to brighten up an area where rudbeckia and heleniums are/will grow. However all the alliums turned out to be purple. An email to the company resulted in a £5 voucher. They don't supply the white any more but I have accessed them elsewhere. basically they wont be in pots very long, just enough to see garden growth, but I will protect them from frost in a cold frame.