I have both of those tents, here are my personal opinions
Niak Pros:
- Free standing
- Can fully stretch out inside and not touch side walls
Niak Cons:
- Location of single door makes entry/exit for more than 1 person a pain because you have to crawl over the other person
- Less usable vestibule space (IMO)
Anjan Pros:
- Easier entry/exit for two people
- Most likely more windproof due to tunnel design. I've been in 50 mph in my Niak just fine though.
Anjan Cons:
- Not free standing
- I'm 6'1" and my feet/sleeping bag touch the rear wall
For my uses, if its just me I take the Niak everytime. If I'm with my wife we take the Anjan. I can confidently say the Niak is the only tent I own that I will never sell.