For those who have been to Argentina, is it easy to arrange tours while there? Or is it better to pre-arrange? We've done both in other countries (Peru was pre-arranged in the US before we left, and in Thailand we arrange tours along the way). We're looking at 'typical' tours. Thanks for any/all input.

book while you are there - you can shop around and do the tour you really want to do and you may also get a discount

I would suggest to book ahead to be assured of a tour and guide if you are going during the busy season and want a tour of several days and several cities. Do you mean tours like city tours or tours of "the north" or do you mean excursions such as boat excursions at Iguazu Falls. I would agree with sashh for city tours or excursions at Iguazu Falls but would book ahead for longer tours.

If you want the services of some guides, specially you should book in advance and make sure you will have the service you want. If you do not mind being mixed and at the end you get what it is available, you can wait until you reach the destination.
Best regards.
Flintstones

Hi there
I'm talking considreing my own experience as a tour guide in BA.
When high season (Oct-March) arrives I became crazy when every day I have to answer to ppl request my service: I'm sorry! I'm fully booked!
Then my advice: Book your tours in advance and relax
Enjoy your vacation!