If you are gaming at 1080p and want ultra settings at 60fps then a 1060 6gb is what you seek. a 1050ti will get you 60fps, but you'll have to make adjustments just to maintain that framerate. I'd skip the 1060 3gb version
On the used or maybe new market if you could find a GTX 970,980 or 980ti those would also be a good choice. A 980ti will give you about the same performance as a 1070.
Another way to boost performance is to run your RAM in dual channel, meaning having two stick of RAM, for 8gb that means two 4gb and for 16GB two 8GB sticks. It's also always better to buy RAM in matching pairs. Also Ryzen CPUs performer better with fast RAM, 3000 is good but 3200 mhz seems to be the sweet spot.
Depending on local prices, probably the GTX 1050Ti. However, if you can find a GTX 1060 (preferably the 6GB model) for a price you're happy to pay, it's a much better performing card.
Now time for me to question your build. Why the 1 8GB stick of RAM, do you not know about the advantages of dual channel memory?
well as for the RAM to be honest i bought the cheapest 8GB DDR4 RAM i could get to build a mining rig..but i never build it so now i will take advantage of those parts...
would you suggest to sell this ram and buy 2x8GB DDR4 RAM like G.Killer Ripjaws or Corsair Vengeance ?
right now i have
1x CPU Ryzen 7 1700X AM4
1x MOBO AM4 socket
and 1x 8G DDR4 2400Hz RAM
i want you to suggest me a reliable graphics card not more than 250 euro or 300 USD
With those resolutions and refresh rates - the 1050Ti would be good.
What is your monitor's resolution and refresh rate?
my monitors refresh rate is 60Hz
and the current resolution i use is 1360x 1024 but its totally ok because is 22inch
the maximum it can get though is 1600x 1200
With those resolutions and that refresh, the 1050Ti would be good for your system.
Ive found some GeForce GTX 1050 Ti 4GB in good prices
a am only checking for ASUS or GIGABYTE is that right?
brands like ZOTAC or Palit i just skip them
do you think that an ASUS or GIGABYTE 4GB will be enought?
oh ok i didnt know
would you say it would be better to get a dual channel RAM instead of the cheap one i already have?
Absolutely. You have a very powerful CPU, and the cheap single channel memory could be halving it's performance. Just on the single vs dual channel, I've seen videos showing the difference with Ryzen CPUs and it can be up to 30% in some games, and this is with fast RAM.