Current compressing techniques guidance

[Spexxos]

I am also trying to get into the whole compression thing. In my case its primarily for compressing savegames. For that matter I would be interested in the current state of things aswell. I think a might be a bit ahead of you in my knowledge, JoeKkerr, and since I dont want to open up another thread with the same topic I am going to add my questions here. I am sure we both can benefit from this. Here we go:

1. What is DELTA and when to use it?
2. When to use what precompressor or any of the programs following? (precomp, srep, pzlib, ztool, xtool, PrecompMT, msc )
I have seen different versions of precompressors delivering different results. Sometimes older versions worked better than newer ones?
3. Why is FreeArc alsways the recommended tool? Depending on my files I got better results with also 7z (lzma2) and rar? Is it because of the ease of use for external compressors?
4. Whats are the benefits of xz? (In my unterstanding its just a container, am i right?)
5. Is there any benefit in using FreeArcs successor (FreeArcNext(?)?)
6. Most importantly: Are there any already written guides that I have missed that have answers to my questions?

Cheers