ASIC (Application Specific Integrated Circuit) server, is a mining machine with chips that are specially designed to mine cryptocurrencies, and they are often pre-programmed to carry out mining for a cryptocurrency. ASIC servers are much more straightforward and user-friendly, almost like plug-and-play with significantly higher returns.
On the other hand, GPU (Graphics Processing Unit) mining comprises of several GPUs (often video cards like Nvidia RTX 3080) bundled together to form a mining rig. GPU mining rigs are less noisy, consume less electricity than ASIC and are currently the most profitable crypto mining option for long term mining. They retain their resell value, even after 4-5 years, as they can be utilized for other requirements and are reprogrammable, which is not the case with ASIC servers.