After Tom Coburn announced his early retirement and the race got underway, I was undecided of what candidate I'd back to replace him (though it wasn't gonna be Lankford for sure). Former State Senator Randy Brogdon who ran for Governor in 2010 (and initially did against Fallin before jumping into the Senate race) gave me pause of who to endorse. There's certainly elements of him I sympathize with as being a strict constitutionalist.
Though when news broke Palin endorsed Shannon, I started to sway over in that direction. Not long after, Erick Erickson followed suit. I personally would've backed Jim Bridenstine my Representative in a heartbeat. Though he's declined to do so, I think he'll most certainly run for higher office whether it's the Governorship in 2018 or Senate in 2020 (or even sooner if Inhofe decides to throw in the towel early like Coburn).
T.W. Shannon truly does listen to the will of the people. While he initially considered backing an Obamacare exchange in the legislature, he immediately turned course when voters spoke their outrage. He's also worked to cut taxes and regulation in his 7 year tenure. Ever since he became Speaker last year, I've paid very close attention to him and have been very impressed. Palin's endorsement already has skyrocketed him up in the polls. Most recent from Public Opinion Strategies shows Shannon down by only 9 under Lankford.
While Lankford has an advantage among traditional cons, I think it's starting fade since his image is being tarnished by his loyalty to Boehner (he'd be so to McConnell too in the Senate). The primary will be held June 24th.