I play siege mostly because the faster respawn time and lack of skirmish phases means I get a lot more melee fights in the same amount of time. As a newer player this means a lot more practice time as well. If duel gave experience, I'd probably play that for the most part, as it was my favourite mode in native.
Siege mode definitely does have a lot of potential for teamwork and tactics. It's not always easy to convince people to follow orders, but when you can, you can very easily and clearly benefit from the team effort. I've seen some fantastic shield+pike walls in siege, and I think support classes have greater potential in siege, where K/D is even less critical for victory. A good leader makes a big difference in siege, more so than melee skill. Battle seems to have more co-ordinated efforts from factions, but I think a dedicated siege clan could definitely pull off some great tactics on siege when banner balance is on. I don't know of any such factions, which is somewhat surprising considering the practical application to Strategus.
I've started playing battle more nowadays mostly because the players are generally much more skilled, so in that respect each melee fight is more interesting and challenging. I've still got horrible awareness and die frequently to cavalry, and archer camping is somewhat aggravating. I figure if I get more practice and get acclimatized to battle I'll start to appreciate it more.
It seems to me that novice players don't like battle because they inevitably spend most of their time dead, and as such move to siege, and experienced players don't like siege as much because all the novice players make teamwork and co-ordination more difficult. Its the players that make the mode, and if more experienced players got together in siege, I'm sure they'd have just as good a time as on battle.
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