I've tried in Daily tournaments but I only ended up in 103 I'm not sure what's the best rank to get rare cards for DT but I have read that you only have a one shot chance and I'm not too sure about elo but I want to know from you guys which game mode is the best ?
ELO Has a higher chance of a good reward. But they are only awarded once a week. Also you have to be good as only the top 100 players I believe are eligible. DT however if you place in the top 150 daily in both Extended and Standard has a very low chance of getting a CR and the better CRs are given to the one in 5 who have the higher DT standing so again you have to be good. There is no easy way to get them unless you are good at making money and buy them. And in that regard I would say Survivor is the fastest way.
Well, imho since DTs are available every 2 hours and it's pretty easy to get into the top 150 (just needs about 20-30 mins), you should spam your chances on those and then, taking into account what xichiteke is saying, spend the rest of the time in survivor and/or ELO
ELO if you're good at this game. Otherwise do a DT top 150 every day, it isn't hard especially when playing Standard.
Player events are the best places to win Crs.
ELO is also good.
DT can be used to get Crs aswell and you only need to get into the top 150 once so you can get a top 150 DT and then spend the rest of the day on ELO.