I'll chime-in on this one since I've become somewhat obsessed with collecting fragrant orchids in the past couple of years: Since you are limited to mail order in Europe, your question is not just which fragrant orchid is easy to care for and worth buying (scent-wise) but also which is relatively common to be available from most growers.
Phaleonopsis are relatively easy to grow and a few are very pleasantly fragrant but none of them have a fragrance powerful enough to fill a room and thus have you and your friends go "WOW!". Forget Paphiopedilums, a few of which are faintly fragrant (most commonly an apple scent) but they're trickier to make bloom (need an annual temperature drop) and you have to stick your nose right into the flower to smell them. Cattleyas have many species that are fragrant, ranging from lemon and roses to what I can only describe as an "old lady's apartment" smell. But Cattleya flowers don't last that long.
So as per previous responses, and with the easy-to-grow and easy-to-find-via-mail in mind, my recommendation is a fragrant Zygopatelum (will fill a room and make you say WOW!), Oncidium Sharry Baby (most commonly described as a chocolate smell but you'll have fun with your friends trying to pin it down) and Maxillaria tenuifolia - smells like coconut and can smell strong enough to be noticed from several yards away.
Finally, if you REALLY want to impress your friends and family, get a Bulbophyllum fragrant species which smell like dead meat, best is B. beccarii - which has been described as smelling like "100 dead elephants rotting in the sun"! From personal experience, it will guarantee you have the house to yourself

!
Best of luck!