Traveling across Europe is an exciting adventure, but staying connected without paying hefty roaming fees can be tricky. That's where e-SIMs come in. Instead of juggling physical SIM cards, an e-SIM lets you activate a mobile plan instantly from your phone. But with so many providers out there, how do you pick the best e-SIM for Europe? And more importantly, when is the best time to buy an e-SIM before traveling to make sure you get the most out of it?