Based on latest Android 4.4.4, Mahdi ROM is a new custom AOSP ROM (What is AOSP?) on the market that brings ultimate performance tweaks along with many customizations. You will get a speedy ROM with a custom kernel that has tweaked governor for added performance/battery life.
I know some of you were having trouble with CM11 ROM last week and since CM11 ROMs are usually works in progress, you may see more bugs until they release stable releases.  Mahdi ROM releases are stable versions so you probably will get much less bugs if any.  Also, Sprint users were having trouble with CM11 last week, Mahdi ROM works flawless on my Sprint S4 as shown in video.
What I really like about Mahdi ROM is speed and performance out of the box without sacrificing battery life.  It’s definitely on on my priority list of go-to ROMs right now.  I first started using on my Nexus 5 and it was one of the fastest custom ROMs for it.  Luckily, Galaxy S4 is actually one of the phones Madhi ROM Team supports right now and you can get it if you have a Qualcomm-based S4 like AT&T, T-Mobile, Sprint, Verizon, Canadian, and GT-i9505.
Mahdi ROM also has plenty of customization/features including PIE Controls, Screen recording, On-The-Go Mode, Immersive mode, Lockscreen notifications, Shake events (for both lockscreen and whole phone), floating Window, and more.
And yes, I get this question all the time but WiFi tethering works out of the box for all carriers on AOSP ROMs.  That’s a given for all AOSP ROMs so you should not worry about that.
Overall, I really, really, really dig Mahdi ROM.  A new custom ROM on the Galaxy S4 market right now and they are doing many things right, bringing users stable, fast custom ROM with great battery life/features.  So if you are in town for one of the fastest Android 4.4.4 ROMs, give this ROM a test drive over the week(end) and do let me know how much you like it!

Download:
Download Madhi ROM for Galaxy S4 (for all Qualcomm-based S4 like AT&T, T-Mobile, Sprint, Verizon, Canadian, and GT-i9505)
Download Android 4.4.4 Gapps (DO NOT USE OLDER GAPPS!!!)
To install, reboot into recovery, make backup ROM, wipe data/factory reset, install ROM, install Gapps, and reboot. (If for some reason you end up in a bootloop, reboot into recovery, go to Advanced Wipe for TWRP or Mounts & Storage for CWM, format/wipe /system, then re-install ROM.)
(First time installing custom ROM? See How to Install Custom ROM on Galaxy S4 first!)
Note: If you have SafeStrap Recovery on AT&T or Verizon S4, DO NOT INSTALL THIS ROM, it will not work.
Credits - XDA <— Please donate to the developer of this ROM or hit Thanks button on XDA if you like it, thx!
Extras:
Want latest Android L Preview Keyboard?  See How to Install Android L Preview Keyboard on rooted Android!
If you want some awesome audio, check out Viper4Audio FX MOD, which you can install on this ROM to enhance your music 100%.
If you want to run your apps in tablet/hybrid/custom DPI mode, see our Xposed App Settings guide.
If you want PIE Controls, see our LMT Pie Control guide.
Q&A:
Q: My 3G/4G LTE data is not working!!!
A: See How to Fix 3G/4G LTE data by Manually Setting APN on Android!
Q: I don’t have Play Store nor any of the Google apps!
A: You forgot to install Gapps, reboot into recovery and install it! (See above for download.)