It's a shame nobody is really using yEnc instead of base64. yEnc only has a overhead cost of about 2%, compared to 33% for base64, and would be perfect for use on webpages.
There's encodings which may be more appropriate, which use more than 64 codepoints, such as base85 (https://en.wikipedia.org/wiki/Ascii85), assuming that these are allowed.
As an aside, I've implemented a fast SIMD accelerated yEnc encoder/decoder here (https://github.com/animetosho/node-yencode), for anyone interested.