In my opinion, ballistas can only be used for defending a castle and for a systematic advance against the enemy. Due to their slowness, you can easily lose out on development compared to your opponent, and stockpiling them in the castle is simply not profitable if you don't use them. It's better to build pikemen (who are excellent warriors with a superb ability) for normal development, and hire ballistas in a separate building, or in a second town (although it's more profitable to build pikemen there if you're already building them in the first town). And I consider the Golden Golem to be the best fighter. It has a very high amount of health at level 2 and excellent stats. It can be used (and should be) as cover for Djinns (although the opposite is also possible: take mages at level 2 - they are good with their spellbook, but they are too weak, and as cover (and not only as cover - for example, with teleport and blessings, send them into the enemy's territory) - nag).

I think that ballistas are actually more useful, at least in the early game. They fight perfectly alongside crossbowmen, but with pikemen, you'll suffer heavy losses; their defense is barely better than that of mages, and attacking through a cell doesn't help much. Ballistas are ideal for sieging a town and for defense as well; if they are placed on a tower, you're in good shape. And besides, if you do build pikemen, you'll have to build monks later, and they are less useful than ballistas; Crusaders are much better than pikemen. Medusas are more practical than minotaurs and more useful in the early game, but I still prefer minotaurs; they have an ability, like ballistas, that is effective against any enemy. I respect golems and build them more often, although mages are one of the best in the early game - while halflings with accuracy shoot down neutral creatures of the first level, mages raise skeletons, which finish off the rest. But in serious battles, mages are practically useless, so golems are better.