It all depends on their team comp and item what is situational, I used to build Seraph before and it was amazing build combined with Luden, tho going with Flash/Ghost is enough good for me, and I don't need to buy Luden.
Rylai gives me hp (survivability)/ap and nice amount of slow when chasing, I won' be ALWAYS chasing ADC and MID with low hp sometimes I they will be dead in fight and I will need to attack their tank, slowing him is something important because you cannot kill him with combo.
I did post few different viable builds,
But I'm going to do some calculations because Abyssal Scepter doesn't give much more damage against enemies might replace him soon in the builds.
Thanks for your comment :)

Indeed it is a bit harder to get much balls nowdays, tho you can get 6 balls without problems with 40% cdr, you have 3 from ulti, use Q, Q, W on first Q, and make another Q, using W on enemy (1st ball from first Q) and you will have 3 on the ground and 3 from ultimate = 6 ), W will now deal more damage (true damage) on target so it compensates loss from 1 ball from ultimate :)

Hello dear Mel0nly :),

She didn't get that much of a nerf, tho yeah it is harder to achieve 7 balls than it was when you could grab 3 balls and secure 7 balls on your ultimate, I kinda like new passive for W now, it gives 20% true dmg which is something that is really nice to have because it ignores all magic resist, so your W can do more damage than it could before, You can still achieve 7 balls while having 40$ CDR by using Q, Q, W ( take first ball ), Q, W and R :), it is harder than it was with old W but I guess that new W does more damage as AoE spell you can do way more damage when you hit 5 people with W example :).

Hey man thanks for your comment,
Let's start with Ludens first, I'm replacing it nowdays often and not building it at all, it provides you with nice amount of AP and movement speed to roam a lot but nowdays as you say it's kinda a bit useless item, so instead Luden I often and nearly always go for Abyssal Scepter which provides me less ability power but gives me nice amount of MR and one of new best passives for AP mids and Scepter has unique passive with her ultimate as it increases damage taken to enemy for each ball you have thrown on him.

Tear of Goddess is something I'm used to, it gives me nice amount of mana and mana regeneration which I use early to punish and bully my opponents which later on gets upgraded to Archangel that gives nice amount of AP and when fully upgraded it gives me shield to protect myself from assasins and those kind of 1shot champions, also combined with Zhonyha you're basically saved from death in many team fights without having support to babysit you.
I usually fully build up tear within 20 minutes.
Thing I don't like with Morello is that I don't get enough mana to spam spells,
But you can always replace my build as I said with those 4 items bellow, you can take Morello instead of Ludens and instead of Tear/Archangel you can take Scepter and continue with Zhonya, Rabbadon and Rilay.
I'm not sure about nerf since I don't play on PBE but I believe you because since last championship people use to ban Syndra 24 7 because someone played her and dominated game, I will still continue to play her even if they nerf her because I like of way how she works, she has unique mechanics and requires a lot of skill to land all 3 spells.

Glad to see that! :) Keep playing her she is really nice champion.

Thanks man, hope you enjoy playing Syndra :)

Thanks man :) really appreciate :)