I use nightly builds of Mozilla. Netscape 6.x is built from the Mozilla source code. Basically NS take the code, apply some rigorus QA and bugfixes, bundle a spellchecker with it, add AOL links and AIM integration.

Mozilla is more up to date because of this, but thats not always such a good thing from a stability point of view. Nightly builds are especially prone to breakages because you live on the bleeding edge. For instance, the email client was broken for a few days a few weeks back. That said, if you dont want that level of bleeding edge, there are the milestone releases. These dont have as much QA done to them as the Netscape builds, but they are more general user orientated (i.e there has been some serious focus on stability).

As for using it, I love it. Its a real browsers browser. i.e. its targetted at you, not some advertiser. Features like tabbed browsing (opening multiple pages in one window- not in the current NS6.2 release) are real timesavers. Pop ups/unders are easily killed with a quick tick in the preferences. Images from servers can be blocked on a per server basis. i.e. ad servers with annoying flashy stuff can be killed quickly and painlessly. (Though I leave targetted content alone by choice, help the webmasters make a living :) )

It feels faster too. Most sites are heavily table based in their layout. IE has to wait for the whole table to load before it can display it's contents. On a 56k modem this can be painful (try reading www.slashdot.org when there are a lot of comments). Mozilla (and NS6.x) display the table as it arrives. With broadband this is less of a concern, and infact I read IE still holds the rendering speed crown here.

The other aspect of tabbed browsing is that on Windows9x platforms it's essential if you want a lot of windows open at one. I generally browse with about 10 windows open. This eats win9x's GDI resources insainly fast. And as a side not, if Mozilla does die, it tends not to take every thing else down with it (because it's not been integrated into everything I suppose).

The major gripe you will probably have is sites that arbitarily lock you out based on what browser you use (never mind that Mozilla/NS6.x could display them just fine if they were given a chance). This is a pain, but I can point you to a tool that lets you alter your browser ID string with just a couple of clicks.

Occasionally you'll find a site that just wont display right, can either be put down to Mozilla being fed a page thats designed for the horribly non standards compliant NS4.x, or the author has just relied on how IE4 displays things. Hopefully these problems will lessen in time. IE 5.5-6 have a very good standards compliance mode, nearly as good as Mozillas standards compliance. In time people will learn to code to these standards, and not to a specific browsers bugs. I'll not lie to you though, for now the problem is still here, though Mozillas broken HTML mode can and does help a bit.

Mozilla is also quite heavy. I dont think I'd try it on less than a k6-2 300. The reason is it's user interface is entirely cross platform compatable. If you ever use it on Linux, you'll be at home straight away. This does however leave it with a performance trade off :( For cases like these people have taken the HTML rendering part of Mozilla (Gecko) and put it insid a native windowing system. k-meleon is one such example. It sticks a pure Windows interface on Gecko, and as such the requirements are lower.

I havn't used IE for about a year now (other than to get to Windows Update). On 9x I used it because of the superior resource management with multiple windows, and more forgiving nature when it crashed. On XP I use it because, well, I genuinly prefer it.

So, to summarise,

I hope this gives an honest impression, other may feel free to contradict me :) Whatever though, please dont use NS4.x . It had it's day many years ago, and it's time to put it down. If it's a choice between NS4.x and IE6, for the love of god use IE.