I have this one by Siemens. It was the only one I could find that had a long wide slot so that I could reheat nan bread in it. Definitely wide enough for a chunky bagel, I'm not sure about a croissant though as I thing it would crush it as the holder pushes together. I has a little rack thing that pushes up above the slot so I suppose you could warm croissants on that.
dualit again - recent purchase for dh for our wedding anniversary. It was expensive - I bought it from armorica which seemed the cheapest online. I bought the combi 2+2 which is different from the standard 4 slot - you get a one slice option (the reg 4 slice just does 2 or 4) plus two sandwich cages. They had free p+p too.
It is very good and we love it a lot!
Holds bagels and thick bread fine and the cages are good when I'm toasting small things (like malt loaf).