Hello
Well all the companies in Sudan ( Sudani, MTN & Zain ) Have 3G network but unfortunately it depends on your location how good is it.
So my advice is check with your friends or where your living & see the fastest. If thats not possible just buy the three companies sim cards it should cost less than five US dollars.
What i did because i hate this, my phone is Sudani because its relatively have cheap calls both local & international but the 3G sucks when i just leave the center by 40 or 50 kms so i got a broadband sim card from Zain & bought a mifi which is a little better with a download speed up to 1 mb sometimes
Hope that helps.
Muhanned