I'd think Angus would be a good cross and should be polled.
I'd also think Shorthorn, especially Whitebred Shorthorn, would be a wonderful cross - but much more likely to be horned. We're still shopping for the next generation of hardy girls for our moorland - we can outwinter 8 on there. We love Blue Greys (Whitebred Shorthorn on Galloway) but they've become very expensive - not surprisingly, they're lovely, docile, good mothers, good milkers, extremely hardy, light footprint, forage well, long-lived, good calves to an Angus, and hence suit this sort of ground in environmental schemes. The only downside is they don't breed young very well; you really have to plan to have a first calf at three years old. We just bought a Luing cross to try, and have a couple of home-bred Red Devon crosses coming through.
Rambling a bit, but with a purpose - I was meaning to show that you might find a market for a Whitebred Shorthorn cross specifically. People like us would only want heifers, but other farms buy BG bullocks to grow on. Worth a thought, perhaps. (And the Whitebred Shorthorn is Cat 2 - endangered - so the more fans and uses it can find, the better
)
Modified to add, I assume the WHS is horned, although all the pics you ever see are polled.