A starbase can defend itself but isn't very powerful. I think that real-time combat is much more exciting. In real-time combat, ships fly around shooting at each other, and their special weapons like missiles and a transporter can have more effect. Unless you have a vastly superior force, you might actually need to use some strategy to defeat the enemy. Real-time combat is especially fun if you customize your ships to use special weapons and create your own battlefield tactics.
Planetary bombardment is a whole other ballgame from space combat.
Unlike in many space games, once you defeat the enemy's ships, you don't necessarily capture the planet. In fact a good planetary defense can destroy most ships. The battle is over when all the attacker's ships and troops are dead or when the defender's buildings and defenses are destroyed. There are 6 rounds of planetary attack to each game turn. Still, on the whole the planetary combat is very cool and adds a whole new level of strategy to attacking enemy planets.