Winger Prospects.
I have signed both in my Chelsea save during different points of time.
Guedes didnt get much playing time because I had a plethora of wingers, I spent about 25+15 mil on him. After loaning him to Atletico Madrid for a year, his price shot up. I got 45+25 mil for him from PSG for him. He wasnt creative in my tactical setup at all on either wing, But maybe I trained him the wrong way. Cant say for sure, What I can guarantee, Is that he will get you a profit.
Zivkovic on the other hand, I sent on loan to Milan, where he was brilliant scoring 8 and assisting 8 while playing in 29 games for them on the right wing. He is a left winger in the game, but I found him to be immensely useful on the right. If you can teach him the PPM Knock Ball Past Defender, he is a beast, will consistently be beating his defender and getting in crosses. Improves slowly first few years, but should replace anyone other than Messi, Hazard and Neymar in any squad.