I probably shouldn't even bother responding to this, but what the hey, I'm bored anyway.

First I must say I don't use Bearshare or Shareaza regularly, as I rarely run the windows operating system on my computer--so I can't respond to the questions about the specific differences between these clients aside from what I know by hear/say. But I can reply to a couple of your questions...

1) Gnutella clients in general should provided reletivly similar results and services provided they all follow the protocol standards. Of course, that is in a perfect world and there are varients, however I have found that both Bearshare and Shareaza have loyal followings who like both clients. I have heard complaints about Bearshare's addware which may turn some people off it. I have also heard a good deal of negative things about the developers of both and how they interact with the gnutella network, although in my experence (mainly using gtk-gnutella) I find that the Bearshare island issue is over exadurated (as their ultrapeers do allow foreign clients to connect to a limited section of slots, and to my knowledge there is no descrimination between clients for ultrapeer to ultrapeer connections. Their clients in leaf mode will only connect to Bearshare ultrapeers though). I have also found that the aggressive approach of Shareaza is over exadurated as well, although I suspect this is because a lot of users don't even connect to the gnutella network anymore, prefering G2/MP and EDonkey.

2) That isn't a question. However yes, Bearshare only accesses the gnutella network, and yes Shareaza accesses all of the networks you listed. In many cases this can be seen as advantageous to Shareaza users, but in other peoples perspectives it can be seen as detremental as the band overhead to maintain connected to multiple networks is higher then simply connecting to one. Personally I'm happy just connecting to a singular network, however depending on the media type some networks are better then others. I still fire up a bittorrent client if I want to download big motion pictures or animation for example...

3) I'm rather partial to gnutella over kazaa myself for several reasons. For one, the open protocol allows me to fiddle around in ways that I simply could not on the closed Fasttrack network. As well on Fasttrack I had huge issues with falsified content which I don't have (as of yet) on gnutella. A lot of people complain that download speed or search speed is poorer on gnutella, but I have not found this to be the case myself. The one thing Fasttrack does have going for it (IMO) is the sheer number of users. It is much easier to find certain concent on it that would be impossible to find on gnutella. That said though, I find gnutella to actually be better at finding rare content in the genres of music and multimedia I am interested in.

and finally I'm not entirly sure what you mean by question number four.

Anyway, hope that helped.

-Kris