Valletta is dense with stone streets and tall buildings. The good news is that both Vodafone and GO have strong signal here, so your MegaEsim connects fast the moment you land and switch it on. You will get clear data for maps as you walk to St John's Co-Cathedral or down to the Upper Barakka Gardens.
Across the harbour in the Three Cities, Vittoriosa, Senglea, and Cospicua, coverage stays steady too. The narrow lanes can drop you to 4G in a few spots, but you will still load photos and messages without trouble. For a few days of light use here, the 1 GB for 7 days plan at $1.29 is plenty.