Welcome to Geekhack!
I'm not familiar with the Logitech K120, but I like MX blacks.
They are linear (no bump, no click) and fairly heavy.
Some people complain that they get tired fingers after long typing sessions on MX blacks.
Really it's up to you whether you like these switches.
Coming from a membrane keyboard, almost any mechanical keyboard will be so much better than what you are used to 
glad hear your answer

so whatever cherry mx switch we choose still more better than logitech membrane keyboard right?

many people said black is worst because require much force (inffective)
,and another say red worst because they're too light and we can't rest our hand onto it because they registered easily(my habbit

)
and another say brown is bad because the tactile bump is annoying
and another say blue is too noisy and we can't enjoyly double tapping on it (i need mechanical keyboard which good at double tapping)
okay 1 vote for black

ps: i'm thin person (about 50Kg) ,
If you have time get gateron black and mod it or just get some vintage black and mod it
My personal experience is pretty good so smooth if you can mod it 
wkkwkw orang indo :v
sorry gan ane masih nubie gk brani mod2,pengennya beli keyboard doang terus brbrpa keycap yg murah2 doang
gue ngincer gamdias soalnya harganya murah tpi fitur komplit + makro pula kwokow
lihat merk lain aduh alamak 1 juta an ke atas,makulm kantong mahasiswa gan hhehe
I started with cherry blacks coming from a rubber membrane keyboard and an apple scissor switch keyboard. It is a great feeling linear switch in my opinion. I immediately understood the appeal of mechanical keyboard from the first moment I tried it. Membrane keyboards have tactile feedback in the form of a bump feel. These will not have that bump. I'm not familiar with how much force it takes to press a Logitech membrane switch but I'm pretty sure it is fairly heavy to begin with. So if it's the only thing holding you back from getting this keyboard then I don't think you will have too much of a problem. Ask them to open a box and try it out a bit in store if they don't have a display model. And tell them they would sell a hell of a lot more mechanical keyboards if they did have a display haha
so you're pleased with cherry mx black? okay i will reconsider it

sadly,the rule in my local store is "if you opened box (sealed) it mean you must buy it"

two vote for black
It's VERY good.
okay 3 vote for black

One man's ideal switch is another's nightmare. For example, raymogi love it, I think it's the worst Cherry MX switch ever made (too scratchy and heavy for me).
Really, you'll want to judge for yourself
.
may i know,how much your weight?
my weight is 50Kg
here my daily usage
1.i like to play moba games (dota 2)
2.make an essay to get my bachelor degree tittle
3.some times i like to play starcraft 2,counter strike,