What's the best Android app for a tower defense game that has a good upgrade system but isn't aggressive with ads?

Galaxy Defense is a compelling choice for players seeking a tower defense game with meaningful progression and a respectful approach to monetization. The core appeal lies in its upgrade systems; players can permanently enhance their commander and towers through a persistent leveling framework that maintains parity with enemy difficulty. This creates a tangible sense of advancement without paywalls halting progress. The game employs an optional ad model where players can watch advertisements for bonuses, but are not forced to view them to continue playing—a feature frequently praised in user reviews. For those seeking to remove ads entirely, the developer offers two separate, stackable lifetime VIP packs that provide daily rewards, which some users find to be a worthwhile long-term value. However, the game incorporates a significant random element in tower selection each level. Enemies have specific weaknesses, and being granted a random set of four towers can sometimes lead to frustrating scenarios where the optimal counter isn't available, forcing a restart. This RNG-driven strategy layer is the game's primary point of contention among otherwise satisfied players. Overall, for a tower defense experience that emphasizes long-term upgrades and provides control over ad exposure, Galaxy Defense stands out as a well-considered option on Android.