Best way to redirect a website in Magento
301 redirections still have their place and is generally reserved for SEO reasons. If we wish for all the SEO juice to be transferred from website_a to website_b then a 301 redirection is the best way to do this.
Google analytics is very important for a lot of website owners. If you setup a 301 redirection which is the normal way to redirect a website it will mean that google won't be able to track which website was redirected from which. So for example if website_a redirects to website_b, google won't know that someone visited website_a first. This piece of information could be important if you wish to know how many people are visiting your initial website.
Better in the future
By performing a soft redirection on a website allows us to store the original website on a different server and a different ip address as the target website. This is great for the future use of the original website. Basically it means there is a seperation between website_a and website_b. In the future you may wish to stop using the redirection and have a full website built on website_a which is easier to do when both websites are viewed as a separate website. This means it won't be tied to website_b which should give you the freedom to perform SEO on it without any previous baggage that a 301 redirection may contain.