What should I choose? A clutch or purse?

you used the word " clutch " so answers put your question an the " car " section.

you need to chose which answers section you want your answer to go in.

But as a man , i would rather a girl have small or tiny purse with a very thin strap. The strap can be almost thin as a string so it is not really that visible

If not she has to hold it all the time and only has one hand.

This is automotive forum but I'm game for answering anything this morning.

If this is a formal or semi formal event (it must be if you are wearing a floor length dress) then go with the clutch. It's more elegant and works better in formal situations. You don't want a bag hanging off your shoulders.

A contrasting color works best. Choose one of the secondary colors on the dress to highlight and use a bag that brings out that color. The bag is an accessory, it should not be the same primary color as the dress.

I don't really like a clutch because it's too small. You should get a bag that's big enough but not too big and not ugly. I think it should match your dress, that would look pretty.