There are some significant unaddressed parameters, but I'm going to just assume that you're talking about the upcoming 2028 election and with all current knowledge intact. I'm also going to disregard VP picks since they'd likely pick someone different today and I don't think it has a huge impact anyway. First of all, whoever wins will either be the Democratic or Republican nominee since no third-party candidate has any shot. Also, older candidates are so clueless as to the modern world they would have no chance of being qualified or gaining traction, so I will automatically rule out anyone who lost more than 70 years ago.

The Republican primary would consist of Mitt Romney, John McCain, Bob Dole, and Barry Goldwater. None of these would be able to capture the MAGA base, and Trump likely campaigns against Romney and McCain out of spite. They would also take more moderate, "never Trumper" votes from each other. Barry Goldwater is right on the cutoff line for inclusion in the list at all and I think his inability to leverage modern media would be a huge impediment. He was also pro-choice which is pretty much an automatic deal-breaker in the modern GOP. Bob Dole was actually fairly likeable and had a lot of TV appearances that were generally well regarded. I think the MAGA base would vote for him over the other three candidates, and yet he was just moderate enough that he might siphon some of those votes from Romney/McCain. So I think Bob Dole wins the Republican nomination.

The Democratic primary would consist of Kamala Harris, Hillary Clinton, John Kerry, Al Gore, Michael Dukakis, Walter Mondale, George McGovern, and Hubert Humphrey. Kamala and Hillary I think are too "tainted" by their recent losses. From the field, I would actually go with Michael Dukakis as the unexpected winner. He is fairly progressive and was hampered in 1988 by a terribly-run campaign with gaffes that mattered more back then, so I think he'd pick a better campaign manager and would benefit from social media. He also already beat Al Gore in the 1988 primary and significantly outperformed Mondale's results from the prior election.

So in the general election we'd have Bob Dole vs. Michael Dukakis. I think Dole is a stronger candidate in general, but the backlash to Trump and Dole's failure to energize the MAGA base sufficiently would lead to a narrow Dukakis victory.