EASY QUESTION! Whatever is easiest for everyone. Email, text, phone calls (GASP!), et cetera.
I've never asked someone explicitly what they prefer, but I find with everyone that they have a method of contact that they respond fastest to.... that is the one I use.
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....For everyone who's talking about how to file text messages and store important ones. I have the solution, I personally do it this way. Not great, but better than nothing.
1) Get Evernote
2) Create folders for the different text/iMessages you'd want to save
3) screen capture your text message conversations (press power button + home button at the same time)
4) upload pictures.
5) Evernote will find the text in your pictures, making your saved messages searchable.
On top of that you can create any tag you see fit..... Evernote really is an awesome tool. Highly recommend!