I am trying to decide which to wishlist and at some point buy.

My gut says Blood Money but others who are much bigger fans of the series overall than myself have pointed out valid counterpoints to it not being the "best". Behind it, I would say Silent Assassin and Contracts (the latter being essentially a remake of the first game/Agent 47). I don't have much experience with Absolution, but the consensus on it being less of a Hitman title and more a weird divergence that just happens to use the Hitman IP is fairly prevalent (though all the games - including the ones not and unlikely to ever appear on GOG - follow the same narrative).

Contracts and Blood Money kinda set the expectation and tone for the series going forward though.

If you don't mind some clunkiness and long & difficult levels, pick up the original. It's the best. You'll get good story too.

If you want more story, pick up Hitman 2. This one has some really good levels and unfortunately some really really bad ones. Gameplay is similar to Hitman 1 but a little less clunky. You lose some features like the ability to purchase equipment between levels.

If you want a polished "classic Hitman" experience, pick up Blood Money. Unfortunately, it's weak as far as story is concerned. More of a collection of random hits. This one is primarily set in the US (unlike the original two which take you around the world), which gives it a different vibe.

If you want a "side story," pick up Contracts. I don't like it much, but it is still interesting, as a fan of the original Hitman, to see the remade levels. No, I don't think they live up to expectations, unfortunately. This is one of the shorter titles, and it's relatively easy too, and there's not that much story innit. Very dark vibe.

All the original titles have somewhat sandboxy level design.

If you want a consolized hollywood style puzzle-sneaker-shooter with mostly linear level design, pick up Absolution. It doesn't even allow you to play in first person. Story has basically nothing to do with Hitman.

Even though everything that happens in it is canonical when HITMAN (2016) begins.

(Something that I do appreciate them doing and not taking the lazy way out and just saying "it didn't happen" even when met with the negative reactions it got)

Yeah, I was in the same mindset before the game released. To be fair, they don't go out of their way to address it as much and in theory players new to the series could start with the 2016 game and be good in terms of non-familiarity with the series' story.

I personally think that Hitman: Codename 47 is the best. Its a little clunky, but it was the first Hitman game i ever played and its just extremely comforting. I think that the fact you cant save mid level means you learn from your mistakes and instead of just going at the same tactic over and over from a save, you have to go through the whole planning and briefing aspect again, which can give you different ideas of how the level may play out, and different tactics to use during the level.

It makes you work out the whole thing yourself, unlike Hitman (2016), and Hitman 2 (2018) where you can just follow a mission story. This game was innovative for gaming at the time, implimenting elements like ragdolls, the disguises and different ways to play each level. As I said it can be a bit clunky, and i gaurentee you you'll have to tweak the controlls, but its a masterpeice, and one of the most reveloutionary games of the early 2000's.

if you like Hitman: Blood Money you'll love this. I still think its extremely interesting to play the first game in a series so notorious and so popular. I highly recommend all of them, but the first, is the best by far!