Suppose you're thrust in a random Fuyuki-style Holy Grail War. Leaving powerlevels aside, which Servant out of the ones we've seen so far would you see being summoned for you (assuming you didn't use a catalyst)? Who would you hope for? Who would you absolutely not want to be paired with?
For my part, I make no bones about it; if I summoned Shuten Douji and she spoke to me as she speaks to Gudao in game, I'd bone her. And then I'd be boned. Or rather, de-boned.
On the other hand, I'd hope to summon Robin Hood. He'd basically do his own thing, I'd support him as I were able, and in the downtime I could make him suffer through Men in Tights.