Employees will usually prefer to be sponsored for a Skilled Worker visa because it leads to settlement in the UK whereas the Senior or Specialist Worker visa is a temporary visa and they have to leave the UK at the end of it.
However, Tier 2 ICT and Senior or Specialist Worker visa holders are able to switch to a Skilled Worker visa which also means that they will subsequently be able to apply for ILR after holding the Skilled Worker visa for 5 years.
For the employer, the Senior or Specialist Worker visa is usually a little quicker and easier to obtain. The applicant also doesn’t have to meet the English language eligibility criteria. However the minimum salary for the Senior or Specialist Worker visa is often higher than for the Skilled Worker visa.