Maybe Absolution if you pretend it's not a Hitman game/aren't a big fan of the series. It does look very nice and was conveniently streamlined for gamers that aren't "hardcore". A lot of people around here are pretty neckbeardy and look down on casuals, though.
Blood Money has the best story and polish, Contracts had the best missions. Either of those are the best of the series but 2 is good, too. The controls are a little dated compared to the latter games so I usually recommend playing it first just so it doesn't feel like taking a step backward if you play it afterward. Codename 47 is only worth playing if you absolutely fall in love with the series and have to play every game. It has some of the concepts the became great in the later games but it's very buggy and unpolished.
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