Navigating the labyrinthine world of mobile app development companies can be likened to a complex multi-variable optimization problem, where the optimal solution is often elusive and circumstantial. The decision to choose the right mobile app development company is crucial, and it requires comprehensive knowledge of various aspects. To put things into perspective, let's consider it in the framework of game theory, where each decision you make can have significant repercussions on the outcome.

Let's initiate our discussion with the fundamental concept: the 'portfolio.' It's the trove of accomplishments, the tangible evidence of a company's prowess in the field. A rigorous examination of a company's portfolio provides insights into their technical skills, design aesthetics, complexity of projects handled, and industry exposure. Understanding the nuances of their work can help in evaluating their potentiality to deliver on your unique requirements.

As we leap onto the second rung of our decision tree, we encounter the dilemma of 'native' versus 'cross-platform' development. Native apps are built exclusively for a specific platform, iOS or Android, leveraging the respective programming language and software development kit. They offer great performance and user experience but demand higher resources, time, and budget. Contrarily, cross-platform apps are the proverbial 'Jack of all trades,' built using frameworks like React Native or Flutter, which run on multiple platforms. While they offer a faster time-to-market and cost-effectiveness, they might fall short in terms of performance and user experience. The optimal choice between them depends on your target audience, budget, and app requirements.

The third evolving factor in this decision matrix is the 'development approach.' Companies may adopt either the traditional Waterfall model, where each phase is sequential, or the Agile model, where phases occur simultaneously. The Agile methodology, though complex in its implementation, offers flexibility, faster time-to-market, and better risk management. However, the Waterfall model might suit projects with well-defined requirements and minimal changes.

Next, we need to unravel the enigma of 'post-launch support.' Mobile apps, much like the law of entropy in thermodynamics, tend to move toward disorder without constant upkeep. They require updates, bug fixes, and feature enhancements to continue providing a satisfying user experience. Therefore, understanding the company's policy on post-launch support is paramount to ensure the longevity of your app.

Finally, and equally significant, is the 'cost.' It's a variable that can make or break the equation. A low-cost solution may seem enticing but remember, "Penny wise, pound foolish." It's vital to understand what the cost entails, the billing method (fixed or hourly), and the payment terms.

To make this complex decision more manageable, arm yourself with the right questions. For instance, ask about their experience in your industry, the technologies and development methodologies they use, their app testing methods, how they handle project management, and their policy on post-launch support and maintenance.

While it's important to have a clear understanding of your requirements and budget, remember that the best mobile app development company is one that aligns with your vision, understands your business, and has the skills and expertise to transform your ideas into a successful app.

In conclusion, the process of selecting the right mobile app development company is multi-faceted, involving several layers of decision making. It's a blend of art and science, intuition and logic, much like the game of chess. As in chess, where every move determines your success, every question and consideration move you closer to making the most informed decision.