Wriggles is better than bloodthirster like 4/5 times.
Bloodthirster needs stacks and yes, they made it easier now but the life steal is less broken. Wriggles also gives you armor, which makes you a lot more tanky and the dmg on it also helps you win skirmishes. Then to top it off, how many times have you missed a lastie by like 5 hp? Wriggles solves that very often. It's also way cheaper.
Blood thirster is good if you're a ranged AD who is just monstering up the lasties or your entire lane and you are sure you can keep it up. It gives you much less survive-ability than a lantern, especially now. The armor and life steal combine to keep you alive longer than the lifesteal from the sword.
Also, wards win games :P It really sucks when you find yourself with 0 room to buy wards. this item gives you free wards!
depends on the champ and role
ideally you should be building ie first for ranged ad, but if you need early sustain you can swap in a bt. wriggles gives too little ad to warrant it for a straight carry.
i feel the change to bt was more of a buff than nerf, lifesteal still scales scales off of everything, arpen, attack speed, ad, etc so you can still get obscenely high and fast heals with little actual lifesteal %. half stacks lost benefits you much more unless you never die.