My favorite time.

I love learning English.
Some people say that leaning English is so hard.
They are right.
But I don't agree with them at all. (If they are right you should probably not completely disagree with them, these two statements following one another seem strange.)
I like watching American TV series with English subtitles and chatting with people from different countries and sharing our culture. Besides, when I learn new expressions and phrases, I get excited. These are my favorite times!
I'm looking forward to seeing how my English skills improve in a year.

My favorite time.

I love learn English.
Some people say that leaning English is so hard.
They are right.
But I don't agree with them at all.
I like watch American TV series with English subtitles and chatting people from different countries and sharing our culture. Besides, when I learn new expressions and phrases, I get excited. These are my favorite time!
I'm looking forward to seeing how my English skill improve in a year.

My favorite time.

I love learning English.
Some people say that leaning English is so hard.
They are right.
But I don't agree with them at all.
I like watching American TV series with English subtitles and chatting with people from different countries and sharing our culture. Besides, when I learn new expressions and phrases, I get excited. These are my favorite time what I like most about English! (Just another way to say it. Because you used "these"which is plural refering to "time" which is singular.)
I'm looking forward to seeing how my English skills will improve in a year.

My favorite time.

I love learning English.
Some people say that leaning English is so really hard.
They are right. (or "It's true.")
But I don't completely agree with them at all.
I like enjoy watching American TV series programs with English subtitles and chatting people from different countries and sharing our culture. Besides, when I learn new expressions and phrases, I get excited. These are my favorite times!
I'm looking forward to seeing how my English skills improve in a year.

English is "so hard" or "really hard" - "really hard" sounds better. But be careful, just like 「とても」in Japanese, people use these words too often. You can spice-up your English with words like "incredibly" or "extremely." If you're describing something bad or negative, you could say "terribly."

"Favorite time" - I'm trying to think of a better way to say this. . . I like the suggestion that Xudong Yang made: "favorite moments." You could also say, "These are precious moments."

My favorite time.

I love learning English.
Some people say that leaning Englis is so hard.
They are right.
But I don't agree with them at all.
I like watching American TV series with English subtitles and chatting with people from different countries and sharing our cultures. Besides, when I learn new expressions and phrases, I get excited. These are my favorite moments!
I'm looking forward to seeing how my English skill improves in a year.