There is no difference in terms of the “final” query. The former was the “old” way of querying post meta, before WP_Meta_Query
was introduced with support for more complex queries.
WP_Query::get_posts()
now simply translates meta_key/value
arguments into the new format with WP_Meta_Query::parse_query_vars()
.
Use whichever format you feel suits best for the task.