Lennon is a horrible snide who has been banned numerous times in Scotland for touchline shenanigans. He's also very outspoken, which is a big turn off to many. He's not very dignified.
Bilic's stock has fallen greatly. He had 6 years with Croatia, but managing a national side is very different than managing a club side.
He's done very poorly in his first season with Lokomotiv Moscow, and it's been widely rumoured he may be about to get the sack shortly. They're 10th in a 16 team league with one game left, on 40 points, won 11 drawn 7 lost 11. He's also spent a few bob there too.
He's basically a Croatian version of Mark Hughes, living off a past reputation. As a club manager he has achieved nothing.