Rise of the Tomb Raider, i'm not the AC series' biggest fan but Syndicate was just shite. They managed to make the combat worse somehow and the story was uninteresting. You can tell that the tomb raider games were heavily influenced by Uncharted, but the second one opens it up a lot gameplay wise and goes for more RPG focused mechanics.

I really liked Assassin's Creed Syndicate, but that was the first Assassin's Creed game I've really played. I played some of 2 but not much.

I also think Uncharted is average to good and hardly deserving of the praise it gets, but I really enjoyed the first Tomb Raider. Rise of the Tomb Raider isn't a game that I enjoyed much. I haven't really gone back to play Tomb Raider 2013, but I have to wonder if I just happened to play it at the right time, when I was in the right mood. It is worth noting that Rise of the Tomb Raider does a lot more than Uncharted's linear, cinematic, on-rails levels. It's not an open world game, but you can spend hours in that game doing stuff other than shooting people, and you can fast travel back to pretty much any of the major hub areas to do sidequests, open stuff you couldn't open before, etc. I don't think either game is particularly bad and my opinion on Rise of the Tomb Raider seems to be the exception rather than the norm.

I say get Assassin's Creed Syndicate.

I pick Syndicate for entirely personal reasons, i played it and liked it a whole bunch on PC but i like AC games so go figure, i played through the first of the reboot Tomb Raiders and while i recognise it as a good game, the animation quality was off-putting throughout and i absolutely hate Camilla Luddington's voice... when the new game was announced with the promise of more of the same i said no thanks.
Lots of people put it in their game of the year awards though so it's probably fantastic if you arn't me :P.

FYI the version of Assassin's Creed that comes with all of the DLC is also on sale for just an additional $6 ($36 total), so you may want to opt for that version if you end up choosing Assassin's Creed.

Personally I'd say Rise of the Tomb Raider is a better game, but based on how you enjoyed AC 2 and Brotherhood, I'd say Assassin's Creed. I really enjoyed AC Syndicate. I'm a big fan of the series. I've played them all except for Unity. AC Syndicate is probably my third favorite in the series, after Brotherhood and Black Flag.

Syndicate is in many ways like an updated take on Brotherhood. It's the best Assassin's Creed game in a while.

Rise of the Tomb Raider is the better game, but it has a bit of Uncharted feel if you weren't into that. The "parkour" aspect of Uncharted is toned down a bit and a little more involved, but I wouldn't go in expecting it to drastically change your opinion on that type of gameplay. The gunplay is not great, though the other combat mechanics are solid. I liked it quite a bit and think it's the better game, but I don't think you'd go wrong picking Syndicate if you're more into Assassin's Creed.

The poll is likely to go in Tomb Raider's favor, so don't entirely go off of that. It's the better game though IMO, but they're both 4 star quality games. I wrote reviews on both of them here and here.

I thought Tomb Raider was a much better game. AC Syndicate is also quite good, but it still has too much open-world-jank for my tastes.

I enjoyed Rise of the Tomb Raider a lot, but haven't had much interest in the Assassin's Creed series since AC3, so take my opinion with a grain of salt. RotTR is a gorgeous game, and I think it handles exploration, challenges/collectibles, and even stealth combat better than recent AC games. In terms of narrative, it doesn't accomplish anything more than the 2013 reboot, but the world and mechanics are done well enough where that's not really an issue for me.

Easily Rise of the Tomb Raider. Syndicate was an improvement for the AC series, but not by much.

AC Syndicate is the best AC game since brotherhood. Main missions are lite hitman-ish style assassinations . The visuals are really good, the characters are decent and the overall story is not trash. It just has the atmosphere man , the Victorian London at night is I sight to behold. This game is a return to form for AC games.

Now RIse. I really liked 2013 reboot of tomb raider. It had nice visuals, and horror-ish vibe with nice gunplay and overall feel of desolate island. The sequel has couple nice things. The cutscenes are very nice and Lara's model is just absolutely amazing, from gameplay animations to cutscenes motion capture and the hair tech is best tech I have seen. Nearly everything else is worse. The story is even worse, the writing is horrible. The gunplay is weak, guns sounds like shit, the hub areas has too much padding there's no sense of place and atmosphere. Lara is even blander. The visuals are a mixed bag, so much pixel crawling and aliasing and the colors are so god damn brown and dull.

Get Syndicate.

I liked AC: Syndicate a whole bunch, but Rise of The Tomb Raider is a hell of a game, imo.