There are different ways to go about it, depending on your definition of 'best'.
You can use Excel for data collection and save it as a .csv or tab-delimited text. That is a quick flat-file upload/FTP solution. Not pretty but very low-cost.
You can use "SAP.Functions" (the VBA object) to do an RFC, in which case you have to provide some macros. This can be nice if you design it well and consider Add-ins for the RFC with nice custom UIs (buttons, fields, etc.). There are limitations though because the VBA RFC solution for example does not allow for a type STRING parameter. Also, changes in Office 2013 made some macros (that worked on 2007 and 2010) fail a syntax check. If your RFC macro is affected by those changes, you may have to deal with lots of patches during an upgrade. This may not be the last update of Office, so that risk is always present.
You can save the Excel as a 2003 XML. I like this one because it looks like Excel to the user (including formatting) but can be read as XML. No need for a separate file (like .csv or .txt). It will not allow for macros in this format though. The saved file would require a flag-file upload or FTP and processing via XML in SAP.
You can use Adobe Forms (TCode SFP in SAP) using the interactive and dynamic forms. This looks great to the user and can be read as XML on the SAP side. However, the downside are licensing fees per recipient and the fact that dynamic forms don't work in the Apple world (iOS). You can do static forms, but they are much harder to handle because you cannot really link the entered data to the fields they go with. You have to be creative to find a way... Adobe Forms may require the installation of designer software on your PC.
Lastly, you can think about a solution e-mailing data to SAP, which requires a lot of setup in SAP and in your company's mail server. Then you have to come up with a good way to route the mail to the proper processing class. You don't have to deal with files, but you expose yourself to all the risks of e-mails (delays, undeliverable messages, third party spying).
I have done all of the above, and each one has its use.
Regards,
Wolfgang