what fans should i get to replace with the stock ones of the nzxt phantom



The 200mm fan spots on the case only support NZXT FN and FS 200mm series fans. This is due to the size offset that they are. This is the only spot to get the FS series fans as they are no longer produced. http://www.performance-pcs.com/catalogsearch/result/?q=NZXT+FS+200

As for the 120mm fans. You can pick up any unit and it will work correctly. Just depends on what you want to spend.
 
I personally like to stick with the same brand for as many of my parts as I can. I have a Phantom 410 and put 4 120mm NZXT FZ Series Blue led fans and 3 140mm NZXT FZ Series Blue led fans in my case. The fans that my case came with were pretty good, but they weren't as good or good looking as the FZ fans. They also come in green led if you want to give your case some flare. I would also recommend putting as many fans in as your case can hold. Your case has 5 fan controllers, so you don't really need to worry about the whole air pressure thing cause you can just lower the speed of some to lower the pressure or vice versa. You will also want as much cooling for those two beast as you can get.

If you don't like the NZXT fans, the Corsair Air Series case fans are a nice choice. They look, work, and are built very well. They are a bit pricey though, but it is easy to fand a site like NCIX or Directron that have them at a discounted price. Amazon price matches these sites, so be sure to see if any other site has the fans you want at a cheaper price than Amazon and price match them.

Bearings also play a very big part in choosing fans. If you can, I would go with ball bearing fans as apposed to sleeve bearing fans. Ball bearings last longer and generally work better. You can find out the bearing type by going to the manufacturers site and checking the specs on the fans.
https://www.youtube.com/watch?v=ORPfV5VC_dU
 
Like I said, as many fans as your case can hold is what I would do. Your fan controller can turn them down if they are a bit too noisy for you.
Bigger fan sizes are quieter than smaller fan sizes because they spin slower, but bigger fans move more air, the trade off is power usage (which is nothing worth worrying over) and cost(maybe a $10 difference at most). Your case can hold 1 front 140mm, 1 rear 120mm, 2 120mm and 1 200mm on the side, and 2 top 200mm according to the specs page, correct me if this is wrong. I would recommend filling all of these slots.

I'm not sure if cost is a problem for you, but if you are on a budget, 1 front 140mm, 1 rear 120mm, 1 side 200mm, and 1 top 200mm will be more than enough airflow for your case. 2 200mm on the top would pull any and all hot air out of that case and the extra 2 120mm fans on the side next to the 1 200mm will be great for keeping your gpus running cool.

I don't really know too much about those fans, but if you have heard great things about them, then by all means get them. As long as you are happy with the product, that is all that matters.
 


what about the h80 fans
 
I read up on the h80 and it seems like a lot of people are complaining about how noisy the stock fan is. It seems like it performs just fine, it is just noisy. I have read some great things about the Noctua NF-F12 fan. It seems that a lot of people use it as a radiator fan because it performs well and is very quiet.
http://www.newegg.com/Product/Product.aspx?Item=N82E16835608026
I will say, though, it is very ugly. I personally would want one that is aesthetically pleasing, but this seems like one of the best fans for a radiator right now and you seemed interested in Noctua fans.

If you decide against the Noctua, do some research into radiator fans. Many manufacturers make fans that are optimized for radiators, like the NF-F12. These fans have high static pressure. If you are interested in learning about static pressure, check out this video by JayzTwoCents
https://www.youtube.com/watch?v=gXAFYNE7Cl0

If you don't really care about all the numbers and stats that companies give to their products and just want to know what the best fan for your radiator is, I would recommend the Noctua NF-F12. There is no such thing as the best fan, but that one seems like the closest thing to it according to a lot of very happy owners.