Personally, I HAVE to pick the two guys on your list who were not, nor ever were professional wrestlers. Call me crazy, but I think the main event of WRESTLEmania should feature, y'know, WRESTLERS... At least the others that have been mentioned worked their asses off for years with one goal in mind of main eventing a Wrestlemania, whereas Mr T and Lawrence Taylor basically walked in and were handed one of the biggest honors in the business. I wouldn't have had a problem with LT vs Bam Bam as the opening match or as an attraction match, but to put those two guys in the main event of the biggest show of the year was just a ludicrous decision. The main event of Mania 1 could have easily been Hogan vs Piper with Orndorff and Mr T in their respective corners; there was no need to put T in the ring.
Honestly, I'm very surprised to hear names like Yokozuna, Sid, Foley, and Slaughter over LT and Mr. T. My take is, at least the 4 mentioned above are legends in the PRO WRESTLING industry.
As for who I believe deserved to headline a Mania, I would have to go with Owen Hart. There were two viable years to have Owen/Bret as the main event of Wrestlemania, but WWE decided to go in another direction (the wrong one imo). Wrestlemania 10 of course saw Bret Hart defeat Yokozuna for the World title, but earlier in the night Bret was defeated by Owen and there was always an opportunity there to pull a Mania 9. Bret was being billed as "the most fighting champion of all time", and he DID lose to his brother earlier in the night, so why couldn't Owen come out after the match and challenge Bret right there to a title match? Bret could have accepted and beat Owen to cap off a nearly perfect night, and it would have done wonders to put the debacle of last years finish out of everyone's minds. Wrestlmania 11 saw a great opportunity as well seeing as the Hart brothers animosity was at its height and the crowd was really invested in, but Bret ended up facing Bob Backlund and Owen ended up teaming with Yokozuna. I have no clue how WWE let this one go; Mania 11 with Shawn/Diesel and Bret/Owen as headliners could have been spectacular.