What competitive positioning frameworks have worked best for you - i.e. standard/academic frameworks tweaked to your requirements or a completely redesigned framework that is proprietary

I'm not sure what "academic" frameworks exist for competitive analysis, but I have worked with dozens of companies and haven't seen a lot of variation in how they approach competitive work. There are three distinct workstreams:

1. Competitive analysis: Building an accurate understanding of how you compare to your competitors. This involves identifying the key capabilities required by your buyers (and important to their buying decisions) and doing research to analyze how you and your competitors stack up. The deliverable is a comparative analysis along with a high-level summary like a SWOT (strengths, weaknesses, opportunities, threats). The audience for this deliverable is primarily product management, engineering, and marketing.
2. Competitive positioning: An exercise to identify a strong position for your product, where it is differentiated from competitors and where this differentiation matters to your target buyers. The deliverable is a positioning document and the primary audiences are product marketing, product management, and some executive leadership (e.g. engineering). 
3. Competitive sales tools: These sales tools make the competitive positioning actionable for the sales team working an opportunity. Aside from just telling them where you are strong, they would include not only feature comparisons but also questions to ask buyers, features to demonstrate, "trip points" to plant, etc. The deliverables are typically called cheat sheets, kill sheets, or similar names, and the primary audience is sales.  

Sometimes people confuse these workstreams and create deliverables that try to serve multiple purposes. Even though the work overlaps from one to the next, I think it's important to recognize the distinct audiences and create deliverables specific to each purpose. 

There are a lot of great existing competitive positioning frameworks out there. I think GTM maturity of the company and primary audience & execution priorities should be considered in designing your framework. I don't always stick to a proprietary framework, I tend to stay agile to my stakeholders. Some best practices:

1. Competitive enablement for sales should be a GTM priority. If the sales team is already adhering to a specific selling framework, I recommend aligning with their common methodology as much as possible to increase adoption.

2. For a more in-depth competitive analysis, aligning competitive comparisons to phases of the workflow of a product helps to articulate clear differentiation based on user needs.

3. Overall commercial competitive positioning should stay high-level and succinct. The more internal, forward-looking product strategy positioning is best staying separate as it is often complex and not the right message for all levels of the sales team to combat competitive concerns in the field. This divide is most common in scaling orgs with an evolving product-market fit.

I generally start out with a very simple, standard framework for a battle card. Then, I present it to stakeholders for feedback. Generally, they find some fields in the framework to not be useful at all, and they request additional information that will be useful to them. The framework you use will be different based on your market, your sales team and the sophistication of your knowledge. 

Another thing to add here – your positioning framework is only as good as your team's ability to find, use and update it. I would prioritize access to information over a consistent framework every single time!

This would definitely depend on the maturity of the company itself, for example, a pre-seed company would have different needs than Series B or series D.

The best thing to do at the start is to capture the baseline KPIs and objectives, clarify the goals, and then work backward on how to achieve them, what tech stack you'll need and which team-members to pull 

How this looks like in real life is, you'll do a bunch of interviews with sales, marketing, product and customer success teams and then tease out the right positioning, establish a persona, and messaging around your department and around your product. 

Then you'll find your top 3-5 competitors and build comparison sheets and battlecards. Share those with your sales and ping them to check their confidence levels and in cadence check the win/loss analysis.

Last but not least, having some social listening tools and keeping tabs on your competitors is also important since you can react just-in-time when they slip. I'd also establish a weekly internal newsletter to share what's going on out there in the competitive landscape so everyone is aware. 

The result after all of this will be a specialized playbook that you can execute on other departments and products in your organization.