Who plays with AMD card with 4gb?

The same confusion can be applied to stuttering - some people say that they play with mediocre PCs without stuttering while others with GTX 1070/1080 say that they stutter. I'd recommend checking Mass Effect PC Performance Thread on NeoGAF - people are complaining since the release about stuttering even on powerful rigs.  

The fact is that in sheer theory 4GB of VRAM should be more than enough for 1080p gaming. But as I said, I have GTX 970 with 4GB VRAM + 8GB of RAM in my PC and Andromeda stutters. Same for my girlfriend who has very similiar rig (i5-4460, 8GB RAM, GTX 970 4GB VRAM) - she has a lot of stuttering too. Maybe it's not a problem with VRAM but with RAM. I don't know.

Personally I don't even play on Ultra (only textures, because otherwise face textures get blurry in cutscenes even on High textures), rest is set to mix of medium / high. Sometimes the game works fine, perfectly smooth 60 FPS, otherwise it stutters. It stutters especially after going to new place after few hours of playing. It becomes unplayable. To me it's a memory leak in the game. Maybe if I had 16gb of RAM instead of 8gb it would help, but I've seen a lot of complaints even from people with 32GB of RAM so... Some people said that they saw RAM usage (RAM, not VRAM) at 25GB! Let me put it this way - Andromeda is not a good choice to base your shopping requirements. 

Rest of the games work fine, so yes, in theory 4GB is enough and any stuttering in Andromeda is caused by lack of optimization (to compare it to you, I can play Inquisition with NVIDIA DSR set to x2.00 so the game is scaled down from 1526p, with everything on Ultra except MSAA at stable 30 FPS without ANY stuttering AT ALL, if I set it to 1080p and mix of high / ultra then it's perfect 60 with few occasional dips). I also don't have any stuttering with newer games.

So yes, all in all 4GB is enough for 1080p gaming, assuming that the game is optimized. Andromeda, in my humble opinion, is not optimized YET. However If I were to buy a new GPU I would aim at 8GB VRAM but that's just me. Maybe I'm not exactly objective because I like to play Skyrim, Fallouts, Dragon Age Origins and other older games heavily modded, especially with the textures, and in these cases 8GB of VRAM is very helpful. It's also future-proof, especially if you don't plan on changing quick. I use one GPU for 3-4 years, but if you're willing to change your GPU next year, then you can go for 4GB. There is a lot of stuff to consider

Decent fps in high resolution is what I am after on very big screens in that department AMD performance is better than Nvidia's.  Nvidia is good at raw fps performance I don't care diddly squat about.