I am looking for opinions on rod lenght. I understand for crankbaits, the longer the rod the better or distance. Perhaps also true for spinbait.

What about soft plastics, jigs, etc.?

Is a 7' rod always better?

I think that between 6'6" and a 7' a lot of the time it is going to be personal preference.  It seems like to me you are correct, most will prefer the longer rod for crankbaits, especially large or deeper ones.  Froggin, pitching jigs, and swimbaits also seem to be be better suited for many with longer rods.  The only thing I personally prefer a 6'6 or shorter rod for is skipping plastics and other lures. 

I like a 7' rod over a 6'6" in every situation except jerkbaits. I find it easier to work jerkbaits with the slightly shorter rod. I just feel I get more out of the 7' rod in casting as well as line pickup for hook setting.

In the end though it is personal preference.

Personally, I like a longer rod for everything.  I have all 7'+ rods with the exception of 3, a 6'6'' lightening rod spinning rod, 6'6'' pro qualifier, and a 6'10'' carrot stix gold.  The first two were basically my first actual bass rods but once I started with 7' rods, any shorter just felt insufficient.  I use my 6'10'' for jerksbaits and topwater but it's because of the action and shorter handle that makes it easier to work both.

It really boils down to your preferences.

Personally I prefer 6' and 6'-6" rods for most fishing. The exceptions are froggin' and C-rigs. My 7' rods usually stay home unless I'm planning on doing a lot of froggin' or c-rigging that day. Otherwise I just use shorter rods. I do have some nice IMX and Legend Elite rods in the longer lengths and I've tried using them more, just find myself putting them down and using shorter sticks. I guess it's what you get used to.

I prefer longer unless I am in/under trees.  However, I feel pure personal preference.  IMHO, the shorter rod can help with tip down and keeping the surface relatively calm for jerkbaits and some stick-top waters (spooks/walk the dog, sub-surface, etc.) where you don't want the line slapping the surface a lot. 

Another thing with the longer rod - and why my preference - is that you can make a long rod cast short - can't make a short rod cast longer   .  Feel I am just as accurate with a 7' as compared to 6'6" of shorter.

I use a MBR 783 (6'6") for close range spinnerbait fishing - around cover, docks, etc.  I also use a CR 722 (6') and MBR 782 (6'6") for many smaller shallow cranks, jerkbaits, and topwaters.  I use the BCR 802, 803, and 804 (6'8") for many jigs and soft plastics for pitching and other close range applications.  It is personal preference, but I don't think a 7' rod is ALWAYS better.

As far as casting rods go, I prefer a 7'+ for almost all applications. There are exceptions, though. I like using 6' 6" for close quarter roll-casting around docks and emergent weed edges, and also for lures that perform better with a downward snap of the rod, like jerkbaits and topwater.

This has a lot to do with what's comfortable, and that's directly related to a persons height and arm length, IMO.