ReBoot

First and foremost, let me say that I accept that a "direct continuation" of the five films isn't happening.  As much as I'd like that, the series got stuck with the same problem that Sonic the Hedgehog did, that Sliders did, etc...notably, ending on a cliffhanger, probably trying to entice a renewal.  That happened, and it makes for a nasty workaround, butit can be worked around and revisited later, either in flashbacks or through indirect detail-filling.  I suspect that people want continuity with the old and some sense of resolution (an establishment of approximately what got us from there to wherever we end up) more than they need a direct "next scene" to be produced.

With that out of the way, I will also say that, as much as I've been waiting for and hoping for a continuation of the series, there are forms of it that I would sooner see the series remain a part of the past than see it come back in.  There -are- such states, and I'm not ashamed to say that if the new series were to, theoretically, be bad enough, then it would be better off not to bring it back from the dead.

The five pitches break down into three categories: Viable, viable with work, and non-viable.

Viable Pitches
Of the big five, the strongest in my mind is definitely Reboot 2.0.  There's a lot of room for connecting the story, the characters are almost all carry-overs (with a few new add-ons), and most importantly, there's nobody missing.  In spite of a bit of disagreeable art (the Bob stuff comes to mind), this pitch is excellent.  Now, it does need some work, but from what I can tell, the authors are willing to do that work and connect some dots for us.  So it's off to a very promising start.  Also in its favor is the fact that the characters aren't entirely redone, and the fact that it could very credibly be connected to the end of S4, with the details filled in quietly.

Viable-with-work

The second-best pitch, in my opinion, is Reboot Regenerated.  The big thing that it is lacking is any familiar characters.  Also nagging here is something of an anti-corporate tendency that just doesn't sit well with me; that's entirely personal, but it weighs in here.  I'll note, though, that I consider that to be far from a deal-killer.  Basically, if you can get the old characters in here in some form (exiled from Mainframe, refugees from the collapse, etc.), even if you spread out the focus a bit, it works.

 The Last Guardian also needs a major overhaul, though I'd consider it to be salvagable.  The child of Dot and Megabyte plot point, as central as it is, has to go...that has the feel of some particularly rotten fan fiction.  Bob and Dot?  Yes, that works, too.  Them being a couple is hardly the most unbelievable thing; putting Megabyte into a love triangle there is a deal-killer, however.  Note Dot's reaction to when Megabyte appeared at the wedding and extrapolate from there.  The work needed here is significant, but it's not impossible, and I think this could be made to work...but if it's going to get anywhere with the fans, it'll have to get over an initial handicap of feeling like atrocious fanfiction, and avoid falling into any of a slew of traps that could kill it.  There's a lot of risk here, and not much reward, but it could work.

 Dead-on-Arrival Pitches

The Last User and Arrival strike me as pitches that aren't going to go anywhere.  As bad as The Last Guardian is at first glance (and I nearly dropped it down here), it can be saved if the authors are willing to shake things up massively.  With these two?  Probably not.

The problems with these two are rather simple: They go against what's generally been established, and they feel like so much science fiction already out there.  I'll grant that 2.0 feels like 1984, but you can use that as a base and work from there; also, it's credible with the "givens" already out there.  In both of these cases, however, you violate those "givens" (user-sprite interaction, notably, hits me wrong) as well as wandering into some really uneasy territory that feels like either The Matrix or Independence Day (or another Sci-Fi film).  These have the feel of needing to start from scratch instead of a rewrite, but that's just my feel.

Closing Notes

I realize that any of these can turn out badly; other than 2.0 and, if it recieved decent amount of work in order to at least get the original characters in, Regenerated, all of the others really don't hit me well.  On a scale of 1-100, with the best pitch of the five being a 100 and the worst being a 1, I'd rank it as follows:
2.0: 100
Regenerated: 50
The Last User: 10
Arrival: 10
The Last Guardian: 1

(Yes, The Last Guardian comes in last despite me listing it as salvagable; that's just an indication of how bad the current form is, IMHO).