The exchange is your best and most reliable bet. Their fee sucks. It is 23% of your purchase price. Although, it is the only true guarantee you've got if buying reserved searing. They are e-tickets and you swipe your card when you get there and they print the stub.
Gen admin tickets...they only let the first 5,000 fans in line in (at least they claim this online). Not knowing for sure if you will get in isn't worth it to me.
The scalpers were mainly selling GA over the weekend but I imagine that has changed as teams get knocked out.
Your last chance is the lottery line the day of the event. I got lucky for the first game and my buddies did it again the second game and were lucky as well.