As far as I played in several servers, I figure this thing out.
There are three possible combination to these two research: Siege Warfare and Curtain Walls. In order to make all the reader able to understand easier, I will provide this guide in tables.
(Note: all the level posted below is just illustration, and it's make no difference
|Curtain Walls Research||Siege Warfare Research||Result|
|Lv. 54||Lv. 56||
Siege Warfare research is higher, which will gives you more chance to raze other people's building while PvPing, but your building is somehow weaker.
This combination will gives you more prestige, but in return you'll experience more razes from other people who attacks you. Suggested for experienced player, who want to harvest more silver and more prestige quicker.
In real life, this combination similar like when you invest more money on developing weapons rather than defenses.
|Lv. 56||Lv. 54||
Curtain Walls research is higher, which will gives your building extra defenses, in cost of your razing chance.
This combination will prevent you from most razes, but also will prevent yourself from razing other people building in most attacks. Suggested for people who like to play safe, yet don't need to farm prestige in fast pace.
In real life, this combination similar to investing more effort and money to developing the defenses rather than weapons.
|Lv. 55||Lv. 55||
Both research are balanced. Your building will be razed more often, but you will able to raze people's building more as well.
This combination is the best combination for most beginners. You won't lose too much time on re-upgrading your building, but you won't harvest prestige a lot from razing building as well. In short, there'll be some balance between your time expense and your prestige gain.
In real life, this combination is like an army who develop both defense and weapons, and play safe on each war they had.
Hope this note will be helpful for those who want to find more info about how this two reseacrh works and its available combination.
Keep your sword sharp, and let the battle begins. Play hard, die hard and rule the server :)