BTECs are widely accepted in general and, for some courses, will provide an easier route into a reasonably decent university. However, A-levels remain by far the better choice for people who are not certain exactly which course(s) they would want to target with a BTEC.
As to whether or not "top" universities would accept the BTEC, it would depend on exactly what you mean by top. Many very good universities will consider applicants with BTECs though they may require you to supplement them with A-level equivalents in any prerequisite subjects.