Q. If I only have a limited amount of time, what is higher priority: proper understanding of Krias Shema or proper pronunciation?
A. Horav Shlomo Miller's Shlit'a opinion is that proper pronunciation is essential. Once you read and pronounce the words properly and correctly albeit rapidly, you can use your mind to concentrate on the meaning and kavonos of the words.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a