Seed compost

I get mine from our allotment shop, I think it is called Clover.  Very soft, almost silky and never any bits at all.

We have Clover multipurpose - does the job for me too 

For the last three years I've used Westland John Innes as it's the only one that's shown consistency. Very light, quite sandy and no lumps. Beware of anything that says 'with added John Innes' as it's quite meaningless. The JI compost for seeds and cuttings is a specific formulation and works very well although it is more expensive than most of the alternatives. Because it does contain some nutrients the seedlings do seem able to stay in it for much longer...very important in our unstable climate when you can't always get on the plot to transplant stuff.

I just use ordinary multipurpose, but sieve it for smaller seeds, or if it's lumpy

Same here.

My seedlings have never complained 

tbh I don't think there are many nutrients in multipurp