If you've already signed up for Microsoft Skydrive you can login and claim 25GB of free storage.
Again, it's really whatever works for you. This is a segment where it's not all about space/cost. If that were the case, Dropbox wouldn't be doing as well as it is considering it's pretty much the most expensive of the lot. I use Drive now because I use Google's other stuff, and because it essentially has an Office ecosystem built in, so I don't have to use Microsoft's products. Admittedly, MS's online Office product is more full featured but I don't need/want it.
Does Google Drive do
binary diffs, to minimize uploading when a file changes?
I don't believe it does, but I haven't seen anything about it. I'm not sure if I see what the big deal is in avoiding the full upload of a 30 page document, but then again I'm blessed with really good bandwidth

Looks like I'm paying $20 per year for the Picasa storage. I don't know how it got to this point since it was $25 per year for 6GB of storage when I initially upgraded back in 2006.
Somewhere along the line, it became $5 less per year for 79GB more.
I was going to mention this too. I remember that at some point, the price I was paying stayed the same but I got more space. I wouldn't be surprised if this happened again, and that they're just being cautious for now.