Well 4 years ago I'd say Dan Jarvis, but he's virtually the heir apparent in the party now.
I think that current bunch of 'next labour stars' of Clive Lewis, Lisa Nandy and Chukka Umunna are pretty awful
Umunna and Lewis I can understand (Lewis less so), but why Nandy?
I've never seen anything promising from Nandy, it seems like the media have accepted her as the soft left heir to Corbyn in the same mould as Lewis
Although Clive Lewis is the Ken Livingstone type of leftie in the Labour party-the people on the far right and far left of the party tend to be really polite or completely awful