I think FedEx is probably the best "overnight" courier, and probably cheaper than DHL for one-off shipments (FedEx has been cheaper for me when sending out of Argentina, though due to my mail-forwarding service, DHL is cheaper for me sending from there to here - see below). If you send it first class mail via USPS it will almost certainly get here, but you will wait maybe a week or two.
I don't know how much couriers cost anymore, but it's probably expensive ($60-$80 USD I'm thinking). It all depends on how quickly you need it as to whether or not you send it overnight courier (and sometimes it's overnight, sometimes a second day) or USPS.
There's nothing wrong with sending it to yourself, if you know you will be there to get it, or if you have a portero who's there during the day and can accept it for you. If you have a portero, let him know it's coming and he'll sign for it if you're not around (the courier should ring the "porteria" bell if you don't answer and the portero isn't at the door).
Worst case scenario if no one is there to accept it would be that it goes to the courier's central pickup. That's where I'm a bit more uncertain - FedEx, for example, may be at Ezeiza for things that don't get delivered, but they may have a local substation that holds it. DHL will hold a package at a local substation until you go get it if you miss delivery (at least, I've had that happen twice). Sending via USPS through to Correo Argentina, if you miss delivery I believe it is available at their post office in Retiro on Avenida Antàrtida. You might want to call both to make sure, or surely someone here will answer with more certainty
I'd probably send it overnight courier and watch the website for delivery info and plan to be there all day on the day it hits BA to make sure.
BTW - I have a service called USABox. It's a mail-forwarding service where you can have all your mail from the States sent during the month. I pay $30 USD a month. I get one "free" overnight shipment a month for that price (weight restrictions apply related to price - up to 4 pounds but weight is determined by by weight and bulk) and it costs me another $23 for an extra shipment. USABox uses DHL and I've never had a problem with them. You can see what arrives in your mailbox via pictures sent through email and choose to throw away stuff, or choose what you send down to yourself. They can also be authorized to accept registered letters or anything you have to sign for.
It's probably too late for you to do your FBI report through this now, if you already have the report and are looking for something now, but you might want to keep it in mind for the future of your mail from home. I also use the mail forwarding address as my resident address for banks and credit cards, so things like debit and credit cards go there when I need a replacement (expired, etc) and it all comes straight here to my apartment within a day or two of me sending it.
