Well, this obviously depends on individual preference. So, I’m not sure I should call them as 'BEST WIP’s in the forum, but here is the list of those I have read and totally loved:
Breach: The Archangel Job by @MichaelMaxwell
Life (and death?) of a double agent.
Blood Hunter by @Interestedparty
Story of a Nise guy, who is not so nice.
Through Broken Lenses, also by @Interestedparty.
Every psychopath life counts.
Becoming Guardian by @Latraytray
How good are you at babysitting? Especially if it’s not your own?
Model Citizen : Unmasked by @RenaB
Angsty, emotional, conflicting story with a supernatural theme. Period.
The Shadow Society by @Carawen
Your life is not your own. Deal with it, and also with the shadows who come as bonus problems.
Shepherds of Haven by @rinari
A story of flight, fright, fight and of shaping Your Own destiny.
The Aegis Project by @Scribblesome
You’re Agent 180. A past trauma still haunts you in your nightmares. Add to that, an Angel is keeping an eye on you, but they are not exactly the Guardian angel type.
Warlock City by @Revache.
A warlock with a familiar. Kind of a loose cannon. Yes, we are talking about you.
Special mention : Kriotopia. The name is the best description available. Period.
I’m sure there are many more which I am yet to read. But as of now, these are the WIPs which impressed me.
EDIT: I forgot about these two wonderful WIPs, and I am really sorry. United We Stand by Alex Clifford and Children of God by Rohie are also great, and I am sure they are going to be huge success when they finally come out.