I came across some lightning tags that are still in beta, ex:
lightning:tabset (Beta) etc
Not sure for how long they were in beta, is it advisable to use them for building UI and deploy to production?
If you are building an appexchange application which is meant to distribute for lot of customers ,you can hold off building as it will be painful to upgrade incase the support is dropped .
For your single instance you can use them but caveat is when you run into any issues ,there will be very little support as it might be known issues .A feature in salesforce is in BETA if it has known issues.
If you want be 100% safe avoid them and use regular ui:input or HTML input.
lightning:input has been in BETA for two releases now .