Cabanas Las Lilas can be inconsistent. Went on 2 consecutive nights. Ordered 2 baby bifes the 1st night, both "jugoso" or medium rare. My GF's was quite well done (done on one side, medium rare on the other), mine was as ordered. Mushrooms a la provenzal were great. Next night, she had a T-bone that did come out jugoso and was tasty. My bife de chorizo was good but not as good as others I've had (and for considerably less) elsewhere in Argentina. However, the mushrooms were way oversalted the 2nd night.
As for other dining venues, we had an inclusive dinner at the Park Chateau Kempinski. The beef medallions there were just about perfect. Very tender and tasty - one of the 3 best steaks we had (Las Lilas didn't make that list).
There's a little dinner on Talcapueho (sp - same street as the Kempinski) in the Recoleta called Norte. Excellent food regardless of price. Just ARS 19 for 2 including a bottle of wine.