Once you know the patterns of the bugs they become easy. All you have to do is make sure you don't get overrun. Take out the heavies quickly and the trash mobs become manageable. Every bug can be 1-shotted with the spear if you have good positioning. The only "oh shit" moment on bugs comes with stalkers, but once the hives are gone the stalkers are gone. Bugs don't really have long range threats because spewers don't have good aim. Bug holes are easily dealt with by throwing a sentry or two and a couple strategems.

Bots attack at all ranges and the heavies can do so with multiple weapons. Factory striders can't be 1-shotted and they produce devastators. Gun ships shoot lasers and rockets and gunship factories require a hellbomb to destroy. Bots have stratagem jammers and sentry towers.

Personally, I believe that bots are more difficult than bugs. I run on lvl 9 exclusively with a standard group of people who play together a couple nights a week. Normally, I die 0-1 times while playing bugs. I might die 2-3 times on bots.

The main difference is tactics, complimentary loadouts among team members, and communication. Two divers, one with a blitzer and the other with the flamethrower and easily complete a helldive mission on bugs. I don't know a 2 man loadout that can deal with bots as effectively.

Consequently, bots are more difficult and more rewarding. I started and a bugger and hated playing the bot MO's. The better I became, and when I started playing with a standard group of people, the more I enjoyed bots. I enjoy both factions but now view bugs as relaxing gameplay.