A seed tray is better as it allows more space between seedlings and you are not wasting compost as the roots will not get down to the bottom half of a flower pot.

Try and use seed sowing compost as it is finer and has less nutrients as the seeds should have enough in them to start them growing.

As soon as the second pair of leaves has grown transplant them into another seed tray or small pot using a multi-purpose compost.

just to add the bigger the seed the more depth they will need. so something like a runner bean I'd plant 2 in a 3" pot whilst summer annuals would be either in a tray or the 1/2 deep/squat 3" pots that you often get primulas in. even then they wouldnt be full of compost.

Since I only sow my own collected seeds of various perennials I tend to sow them in 6 inch half pots (Cactus pots I think they are sold as). But then the things I grow need to stay growing on for a long time after sowing so need the extra depth.
As said for plants which are moved on quickly then a seed tray is best and deeper pots for tap rooted things like Beans.

For perennials I use 3" square pots because I don't need scores of plants. Bulb seeds (narcissus/crocus/arisaema etc) go in 3" tall pots, lilies in 3" or 4" squares. These seedlings are all likely to stay in the seed pot for at least a year and get the occaisional feed of weak tomato feed. I don't grow annuals but cabbages and leeks get sown individually in cells or narrow paper tubes. Climbing beans are grown in 2l tall pots and stay in them.

Thanks everyone - v.helpful indeed. I like the maxim, the bigger the seed the bigger the pot/room to grow, that's easy to remember!
Mrs W-M x

i use any size pots for all my seeds including seed trays..it also depends what you are intending to grow.....I usually start about now sowing my seeds ....As i do an annual plant sale in may every year.
Plus once the seeds get to the right size i do put them into a certain sized pot ...It also depends whether you intend to grow veggies in containers