4gb 2n or 8gb.

I don't know what RAM you are trying to compare because both of your links are faulty and the keywords after each don't work in newegg.

I will say that $30 is low for a new 8GB RAM kit. If there is such a price for an 8GB RAM kit then it is probably used and should be avoided like the plague. $30 is slightly too much to pay for only 4GB of RAM. For RAM 4GB should be about $25, 8GB should be around $45, and 16GB should be around $90.

Unless you do huge amounts of compression or rendering I strongly suggest getting 1333MHz or 1600MHz RAM, of which any set should be very close to the prices I gave you.
At that price you could grab two of those 8GB kits. If you wouldn't use the additional RAM with your usage you could use the extra 8GB as a RAM drive for some of your files, you would just need to remember to copy anything you finish using back to the hard drive to retain any changes. I guarantee that the 8GB of RAM would be a faster storage medium than any SSD.

Also consider that that is the cheapest high-quality 8GB kit I have ever seen below $40, there probably won't be any other kits at that price, and it probably won't last.