gpllgpllicensing
From what I've read, LGPL 3.0 allows you to use the license together with other licenses, more permissive about that(Not even sure about that).
From https://www.gnu.org/licenses/gpl-faq.html#AllCompatibility it says that it is not compatible with GPLv2, while LGPL 2.1 is compatible with it. That's a bit contrary to the thing I've read…
So, do you know what the real advantages and disadvantages of LGPL 3.0 over LGPL 2.1 are?
One disadvantage would be that it is not compatible with GPLv2.
From your comments, it appears that you're looking for a way to license a library that you wrote so you can use it in a proprietary project but still have the license be GPL-compatible.
First off, this is a bit nonsensical. The GPL carries a whole lot of anti-proprietary-software ideological baggage with it. It's designed that way; the whole point of it is to make it as difficult as possible to integrate GPL or LGPL code into a proprietary project.
However, licenses are for other people. They don't apply to the copyright owner, which is you, the person who wrote the library. You can use your own code however you want to, regardless of the terms of the license you put on it. So you can make it GPL or LGPL and still use it in your proprietary project and you'll be fine.
On the other hand, if you want people in general to be able to use it in GPL projects or also to be able to use it in proprietary projects but still be required to publish the source to whatever changes they make, try dual-licensing it as (L)GPL and MPL.
Given your description, I think A and B is irrelevant to the question, what matters is C and D, and the question comes down to whether or not GPL allows dynamic linking. If anyone may violate the GPL, it is C if it is not under GPL.
After some digging around, I found that the Wikipedia GPL article has a good summary of the issue. The answer is: it is disputed. The three existing standpoints, according to this article:
Both dynamic and static linking violates1 the GPL. This is the standpoint of the makers of the GPL (the Free Software Foundation), and they created the LGPL for this reason (to allow dynamic linking without violation).
Static linking violates, but the GPL is not clear about dynamic linking: It is hard to tell since the GPL does not provide clear instruction about what is considered derivative work.
Linking is irrelevant: GPL should only apply to source code-level. In my opinion this is the most sane option, since linking to a software to access its functionality is akin to pushing a button on a GUI to do the same thing.
Since the FSF says its intention with the GPL is to disallow both, I think it is wiser to either
respect that intention and use GPL on your own work if you link to GPL, even if the wording is not clear
or stay away from GPL software
Ironically, the GPL is not as free/libre as one would think. I know there is a reason for that, but my point is: don't put GPL on your software without thinking. If you are looking for a free and permissive license, the MIT or BSD licenses might represent your intentions better.
1: when I say "violates" I mean it violates iff the "consumer" of the linking is not under GPL.
Best Answer
I think you have to start with the intent of the LGPL 2.1 and the LGPL 3. The LGPL 2.1 was designed to be a license written largely in plain English that would give programmers guidance on what they could do with the software. It is generally clearer than the GPL 2 because of the linking safe harbor. One major uncertainty regarding the GPL is whether a copyright holder even has an interest in controlling what programs can link to a copyrighted library. The LGPL dispenses with this uncertainty by providing a safe harbor regarding linking.
The major shortcoming of this approach though is that it tends to be dependent on US legal concepts and the like, and jurisdictional definitions. What may be a derivative work in one jurisdiction might not in another and this makes a significant difference when software is bundled and distributed, and permission is given for aggregation but not derivation. The LGPL has less trouble here than the GPL but it is a significant uncertainty particularly in the GPL which is a companion license.
To resolve some of these issues and also provide better controls over exact rights, the GPL v3 series of licenses were drafted (the LGPL 3 is part of that). These seek to do away with jurisdictional definitions of derivation and aggregation and rewrite the language so that it provides guidance for lawyers rather than programmers. The licenses are far more complex, far utilizing structures more accessible to lawyers than programmers, and not necessarily any less vague.[1] However they do succeed to some extent in getting around jurisdictional definitions.
So the first tradeoff is whether you want to be writing your license as one that the audience is a programmer vs the audience is a lawyer and the second is how concerned you are about international definitions in different jurisdictions.
The final one though is that the GPL v3 series of licenses have forced compatibility with the AGPL v3, meaning that code can be taken from GPL programs and have the added restrictions of the AGPL added on in such a way that this cannot be contributed back under the same license. This is an issue with LGPL -> GPL copying as well on either license so it is probably a relatively minor concern.
Myself, I prefer the GPL v2 and LGPL 2.1 licenses because they are simpler and so I figure that there is less opportunity for a major misunderstanding to take place (minor misunderstandings may be more commonplace however), but this is my own personal preference, and yours may vary.
[1] For example, if you read both the 2-clause BSD license and the GPL v3 (and by extension the LGPL b3) narrowly, these licenses are incompatible because the BSD licenses do not explicitly mention sublicensing unlike the MIT licenses and therefore at least some lawyers like Larry Rosen do not believe such of a license is granted. Therefore you can't just take BSD code and relicense it as GPL v3 without actually adding copyright-worthy changes. Yet everyone agrees the BSD and GPL v3 licenses are compatible. This poses significant problems in interpreting the licenses and line drawing however.