Lesnar had just beaten the streak a few months prior so it was hard believing he wouldn't walk out as champion. My initial thoughts were that there'd be cheating involved but Lesnar would still win, or there'd be a DQ/countount finish or something. But not only did Lesnar clean, he won in a complete squash in the main event of Summer Slam. I didn't expect the match to be that big of a blowout and it was pretty crazy when it happened.
Sheamus' win looked like a fluke. He was new to the roster, and he got the opportunity from a battle royal, I believe. I expected Cena to beat him especially with it being a tables match and with Sheamus being relatively new at that point. But then finish happened and Cena just fell backwards through the table and we had a new champ.
I was probably most shocked by Owens going over. Rusev beat Cena in their first match but there was cheating and Wyatt lost to Cena at 'Mania so I didn't think they'd actually have Owens beat Cena. I believe this was also after Cena had beaten Sami Zayn in Canada, and Neville. Don't get me wrong, I love Kevin Owens and his promos leading up to the match were awesome. However I never expected them to let this guy with a fawhawk, large gut, wrestling in a tank-top and athletic shorts beat the top guy cleanly. The match was awesome, and I voted for that.
Tensai would probably be my fourth pick (although Otunga interfered IIRC) as the whole thing felt like a flop as we all knew it was Albert but he still beat the top guy, and everything else I either don't remember or expected Cena to lose whether it was clean or not.