When allocating a budget for paid search campaigns, there is no one-size-fits-all solution. The best model depends on your specific goals, situation, and preferences. Factors to consider include your business model, campaign objectives, data availability and quality, and budget flexibility and scalability. For example, a subscription-based business may have a different revenue stream than a one-time purchase business, thus requiring a different model to optimize long-term profitability. Additionally, a campaign that aims to generate leads may have a different CPA and ROAS than one that aims to increase loyalty or referrals, so you may want to use a different model to align your budget allocation with your objectives and expected outcomes. Moreover, certain models require accurate and reliable conversion tracking and attribution, while others need comprehensive impression and click data. Finally, some models allow you to adjust your budget based on performance and demand, while others require maintaining or increasing the budget to keep or grow market share.