So what is to say about that one?
Pros:

I used to prefer it over the C64S, it just suits me more. I like the styling and the sort of desktop feeling. It's quite comfortable to brows through your directories (there is a bug (feature?) actually, after browsing in a 'deep' directory, and going back, you can't go up (cursor up), you have to go back in the hierachy (cursor left) to be able to go up again, it's a bit annoying). This one never failed me (like some others) concerning stability, it didn't crash my computer even once. But since I've got the registered version of C64S, I've got to admit that I use that one more often nowadays. The first thing one recognizes, is the missing border. If you run both emulators at the same time (or just one after the other), one will see, that the graphics of the C64S are a lot smoother. (they are DOS programs, can't you switch off that HD interrupt?) Overall I would say I'd like to get an emulator with the features of this one and the feeling of C64S...

Well I guess that's the comercially most successfull c64 emulator. It started of as a shareware emulator, as far as I know it sold quite well. As a matter of thanks for many people registering they crippled the newer shareware versions. You are only permitted to try the newer versions for about ten minutes, then it will exit gracefully...
(needless to say I don't like that) (are they hoping for more people to register or what?)
I recommend therefor to get an old version of the c64s as far as I know up to version 1.0c this nice new feature wasn't implemented. Get c64s10cd.zip at frodo.hiof.no/pub/c64/emulator. (there are newer versions, look for them yourself...) They tell us a new shareware (V 2??) version will be out someday, but as a matter of fact, it seems like they are forgetting it... .
I don't know what it's like in other countries, since Germany got another distributer than the rest of the world, but here the update policy is handled very strangely... You have to buy 'tokens' of some kind (by registering you get 3 tokens for 'free'). If you want to upgrade your registered version you have to tell them your token number (which in turn have to be registered), depending on the kind of update you need more than one token... . Extended support too costs one token (again, needless to say that I DO NOT LIKE that).
The current version of the emulator has difficulties with soundblaster settings (I've got a soundblaster pro compatible card), I asked them what went wrong, they said it's a known problem perhaps it will be fixed some day (I didn't have any problems with the old shareware version (DON'T run the config program ever without '-s' option (if you don't want to take a high risk of having to reboot))). They gave me the tip I should put soundblaster settings in the 'autoexec.bat'. Great tip, that I got allready out of the handbook, after all I'm able to read. OK, after they couldn't help, I did a little experimenting. I don't know if that is true for all versions but it heavily seems to depend where in the 'autoexec.bat' the settings are set and in what order they are set. If you do have the same problem just try experimenting with these two factors in mind (eventually it did (and still does) work for me)(there is a third factor, rumors tell, that it matters if the setting are written in capitals or not!!!).

If you close your eyes concerning what I said before, you'll get a fine emulator. I do not feel quite as comfortable with it as I do with PC 64, but once you get it going it certainly does feel more like a C64. It has some sort of fastloader support (V20a) (you can configure it that it emulates a 1541 in all details, including processor...)). It's annoying that you cannot switch between the two floppy-emulation modes online. If a game really uses a fastloader (on your real c64), it will thus be turned into a slowloader (kind of funny isn't it?) (hey, that's just a fact, I can't do any better..).
(BTW, I can't set the default D64 directory, am I dumb again or is it a feature?)
Upon registering you also get a small bunch of utilities with some (not up to date) documentation. (Again, that's just my experience). I like the transfer utility (com1541), though it's documentation is more than spartanic, the program itself even crashed quite a few times... but don't get me wrong, I really like it. (I transfered about 1.000 disks with it, since I was running DOS, some crashing is to be expected). (I'm in a bad mood today, you might have noticed!)
So what is to say about that one (V20a)?
Pros:

If your are still interested, try contacting www.seattlelab.com.
If your are still interested, try contacting in Germany (europe) (email) They got a page:
http://www.phs-edv.de.
They have a 'new' demo there as well as some updates (German version)

Activision Game Pack for C64 (Windows 95)

Interview of Frederic Gidouin [french]
- When did you get the idea to code PaCifiST? And Why? 
- I was following the C64 emulation scene for a long time and about 3 years ago I started one
(E64) to challenge myself. It was very limited, but sufficient to play my favourite game: The
Sentinel. I haven't carried on the development. 
...