Sinister sucked imo, long and slow and saw it all coming. Insidious I loved the first half and lost enthusiasm in the second and third acts. If you liked those two, Mama is better (HBO Go). The Possession was ok, not better than Insidious but not as terribly boring as Sinister.
Personally scariest movie is Jacob's Ladder. Not typical horror, just deep bone chilling psychological horror. If you want clever above all, Cabin in the Woods is a must see. If you're ok with gore that's well done and horrifying rather than just disgusting, the Evil Dead remake is scary, mad gory, and a wonderful big budget retelling of a low budget classic that changed horror movies forever. Actually thinking of it, watch the original Evil Dead and Evil Dead 2 if you never have, it's essential horror movie history.
My favorite franchise is Hellraiser, though I cannot claim that it's a good franchise, it averages out to pretty bad actually. All 9 Hellraiser movies are on Netflix. Yes, nine. Two of them are not bad for their time. Three of them were just random movies rewritten to be Hellraiser scripts. One is a damn Alan Smithee movie. One is an ashcan movie, made only to retain movie rights, meaning it was shot in days and never released, and never really meant for anything. Clive Barker is in talks to do a remake of the original Hellbound Heart. I am excitement.