This is a good question and always pops up in many projects. We always try to look at the customer life time value as the long term KPI. In most businesses 20 % of your valuable customers account for 80 % of the overall sales. It helps to identify those customers, by setting up a clear funnel analytics over a longer period of time and measure each conversion step.
: from visit to registration, to sales, to repurchase and so forth. Also take into account the value of each sale. A customer that had to register to purchase, has shown a bigger commitment and might become more valuable in the long run. Many times it is quite easy to get registrations, what counts is the sales. On the other hand with registrations you have a valuable database you can retarget potential customers. I guess you should try, analyse the results and continuously optimize. Moreover this also depends on your kind of product and the traction you want pursue.

Just look at your ROI return on investment. You should clearly see which way is going to get you the most money the fastest. If you could some how do both methods that would be the best option.

I will suggest you not to get confused between ACTIVATION or SALES. Market favors innovative ideas. I will suggest SALES ACTIVATION. Sales Activation. Igniting sales. This is also a critical and often missed or misconfigured integration between marketing, sales, and technology. Sales Activation happens at the bottom of the funnel during the Decision-Making stage of the buyer’s journey. This is also the place where deals can stall, and sales cycles can drag on if a clear and superior buying option is not presented. Integrated Marketing, Sales, and Technology. A successful Sales Activation program is a strategic, ongoing process that equips business development staff with the tools, methods, insights, and technology they need to provide prospects with the right information at the right time. It is an integrated platform of Marketing, Sales, and Technology that serves up answers, as prospects move forward seeking to solve their problem and/or find the product or service that meets their needs.
You can read more here: https://bigidearesults.com/pipeline/sales-activation/
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath