LOL
You don't have to be wisest to answer it.
The franchise took a few directions and evolution wasn't always positive. I've posted about AC games elsewhere, but who'd find it now.
AC1 - skippit as it's tech demo
AC2, AC:Brotherhood, AC:Revelations - socalled Ezio trilogy actually completes another assassin's story too (Altair) has it's hiccups but "fixes" them throught the trilogy, for example atrocious timed puzzles design from AC2 never appears in other AC games again. These three games are mustbuy and mustplay before you die.
AC3 - I loved it, but many people didn't as it doesn't have spectacular towns like it's predecessor trilogy. Of course it doesn't, Boston was a village back then. But it made revisionists butthurt (saw that word at some JDR's post today so I have to use it). This one has a story twist unlike previous trilogy which is a great thing. Not so great is ending of Desmond's arc. What's horrible is mushoorms emulation on PC in certain minigame. Buy on sale.
AC4 - overrated unoptimized garbage. Don't even think about buying it.
AC:Rogue - a small gem that's sadly very short. Buy immediately.
AC:Unity - not only the worst AC game, but one of the worst games ever. It's mmo where you can play singleplayer. Just as other products advertised as such, scratch that "you can play solo". It's mmo and you must coop with unknown idiots who'll screw your progress in many missions. This mmo has bugs that remained even after numerous patches as if Bethesda developed it. Pretend this turd doesn't even exist.
AC
yndicate - chariot races. If you love need4speed, well then, buy right now. If vehicle races are not your thing, forgeddit.
AC:Liberation or something like that, AC:China, AC:Egypt, AC:Russia… AC
hovelware - phonegames and nintendo gameboy rubbish. Don't bother and don't support bullshit. Voting with your wallet will make Ubi not to make more scams. Hopefully.
AC:Origins - a huge shift to RPG. It's still an environment puzzler, but there are enough RPG elements to call it at least RPG hybrid. Optimization on PC is still horrible, the game hammers quadcore CPU like crazy. But even with that hammering, unlike AC4 where microstutters happen every minute, in AC:O you'll rarely see them. Most of the time you'll be able to enjoy it with smooth 60FPS on PC, so buy. Now please.
DLC… DO NOT BUY. Only AC:Origins expansions are worth your cash. DLC in the rest of AC games is plain crap.