I assume its Adams v. Jefferson. And the latter might actually have a better chance than in 1796 in OTL--the Republicans did well in congressional elections that year,
https://en.wikipedia.org/wiki/Party_divisions_of_United_States_Congresses and while George Clinton lost the vice-presidential race to Adams, he did remarkably well under the circumstances:
"In view of all Clinton's disadvantages--his Antifederalist record, the
dubiousness of his 1792 gubernatorial victory, the lateness of the
Republicans in endorsing him (Kaminski, p. 236, remarks on the logistical
difficulties of Clinton's candidacy: 'Presidential electors were elected
in mid-to-late fall and were required to cast their ballots on December 5.
To inform all of these electors that Clinton was the designated Republican
candidate was nearly impossible.'), the nonexistence of any but the
loosest party organization on a national scale--the surprising thing is
that
"'With their low-keyed, behind-the-scenes activity, the Republicans came
close to upsetting Adams. Although Washington was again the unanimous
choice of 132 electors--two electors from Maryland and one from Vermont
did not vote--Adams had only seventy-seven votes. Clinton, with all the
votes of Virginia, New York, North Carolina, and Georgia, and a single
vote from Pennsylvania, had a total of fifty. Kentucky cast four votes
for Jefferson, and South Carolina produced one vote for Burr. *Had
Pennsylvania swung to Clinton, he would have defeated Adams.*" McCormick,
p. 49. (Emphasis added.) ..."
https://groups.google.com/d/msg/soc.history.what-if/WWdwLlM4lyY/Tjd0fjfn5bEJ
Of course, the vice-presidential candidates also matter, since under the Constitution as it then existed, the man who was intended to be vice-president might become president instead. One surprising possibility, if the Federalists win, is the US getting its first Catholic vice-president--or even president--long before one would think it likely:
"Sounds implausible, but "In reply to a proposition from McHenry to support
Charles Carroll as a Candidate in the event of the President's [Washington's]
retirement, Hamilton observed, 'Your project with regard to the Presidency in
a certain event will, I believe, not have an opportunity of being executed.--
Happily for the public tranquillity, the present incumbent, after a serious
struggle, inclines, if I mistake not, to submit to another election.--If it
turns out otherwise, I say unequivocally, I will co-operate in running the
gentleman you mention as one of the two who are to fill the two great
offices--which of the two may turn up, *first* or *second*, must be an affair
of some casualty as the Constitution stands. My real respect and esteem for
the character brought into view will ensure him my best wishes in every
event.'"
https://books.google.com/books?id=3SQ-AAAAYAAJ&pg=PA59
"If Washington did decide to retire after one term, could we get John
Adams/Charles Carroll vs. Thomas Jefferson/George Clinton--with the
Federalist ticket winning, and with a handful of southern Federalist electors
voting for the Catholic but southern (and slaveholding) Carroll
http://en.wikipedia.org/wiki/Charles_Carroll_of_Carrollton but not for the
northerner Adams, so that Carroll comes out a vote or two ahead?..."
https://groups.google.com/d/msg/soc.history.what-if/Q2atPpnHziE/FCONpGPb60cJ
(Alternately, of course, anti-Catholicism could lead to a few Federalist electors not voting for Carroll, so we could get Adams-Jefferson for years earlier than in OTL. But it's more likely that the Federalists will name a southerner other than Carroll to be Adams' running mate--maybe a Pinckney...)