A resposta certa é cada caso é um caso mas, a edição atual do "Technology Radar" (by ThoughWorks.com) traz uma recomendação de "Hold", ou seja, "espere um pouco" e pense antes de tomar uma decisão sobre Application Servers no seu projeto.
Reproduzo o conteúdo original que você pode encontrar em https://www.thoughtworks.com/radar/platforms/application-servers. Eu destaquei algumas frases ("negrito").
The rise of containers, phoenix servers and continuous delivery has seen a move away from the usual approach to deploying web applications. Traditionally we have built an artifact and then installed that artifact into an application server. The result was long feedback loops for changes, increased build times and the not insignificant overhead of managing these application servers in production. Many of them are a pain to automate too. Most teams we work with favor bundling an embedded http server within your web application. There are plenty of options available: Jetty, SimpleWeb, Webbit and Owin Self-Host amongst others. Easier automation, easier deployment and a reduction in the amount of infrastructure you have to manage lead us to recommend embedded servers over application servers for future projects.