Hmmm. Multiple thoughts.
Mixed mode commuting has changed me from a bike snob to a more realistic biker. I thought I'd want a fast multi-gear road bike that I can fold into nothing. Surprise! Ease of folding, ease of rolling thru the terminal are much more important to me. And for the distances that I'm travelling (typically 2.5 miles on one end, 1.5 on the other), the "most-efficient time" is not substantially different than my "relaxed, I'm not gonna get sweaty pace". If I'm going to work or a social function, I want to arrive calm, cool and collected, not a sweaty mess.
Having owned multiple folders (20" dahon helios, 20" dahon boardwalk, 16" curve d3, strida 3, strida 5, and now a brommie T5), they all have their place. I like the ease of selecting the right gear, but I can make do with a single speed bike. My Strida has circumnavigated Manhatten, with hills and bridges a bit annoying but manageable. For the most part, on sub 4 mile rides, I can do w.o the multiple gears. After that, I'm on the bike enough to miss the gears, and I notice the difference in riding time.
The 3 speed is more than enough for a commuter bike (again, I'm trying to commute w.o. getting sweaty); I do like the closer gear options afforded by 5 or more gears.
Weight does make a difference, but more for carrying it than for riding.
The center of gravity for the dahon's suck for carrying. When the bike is folded, I could never find a convenient way to carry them. And unfortunately on the 3 that I have owned, they just don't roll along nicely in a folded state. So living w them, I needed to attach a strap or put them into a bag to make carrying them easier. This contrasts w the Brompton (which is nicely carryable, though heavy) and the Strida (nicely carryable, and Light).
Strida rolls along nicely in their folded state. My rackless Brompton (with only 2 wheels) doesn't roll along nearly as nicely. You'll prob need a Brom with a rack and 4 wheels to roll nicely in their folded state.
NJ Transit buses are erratic with allowing bikes on board. Most buses will just allow you to bring your folder right on board. Some buses (with the cargo area below) will require you to put your nice bike down below. As a consequence, bring a nice bag, or expect scratches. On rare occasions, the buses w.o. cargo areas will not allow you on at all.
On trains, my strida will fit right overhead in the overhead bins; the other bikes need to be stowed next to you, or you will need to stand at the wider ends of the trains.
Penn station *is* a shlep. You will either need to unfold your bike and roll it along, or get the brom w a rack to roll it along nicely. My strida is the only one that I found to be enjoyable to roll in a folded state for that length of time.