Regarding the attack, you only need to keep one unit of High Middle Age to get the PVP points in High Middle Age Tower.
Trebuchets have slights advantages over catapults due to the extra one range, three attack and one defense that they have. You can keep one building if you have already one or two catapults.
Crossbows are not so better than archers as it needs more space (3X3 against 2X2) and more time to build (4 hours against 2 hours) and less range (5 against 6) have some extra defense and attack is the only advantage, so i prefer archers to crossbows (i have still six buildings of them-it's more personal because I love them). having said that in a very tight fight between a very high rated player crossbows win due to their extra defense and extra attack. You can keep one crossbow unit if u have space and money.
Berserkers are good defenders but not so helpful in attacking due to the less reach. however, they are good against knights and other infantry units. Also, heavy infantry are more or less same, better not to keep (my personal thought).
Knights have better reach but are costly in respect of building size and time to heal or re-make. but you need only 4 knights to defeat 8 catapults in attack due to their high attack, good reach and defense. you can keep one unit.
So in total, the best attacking units to win most of the fight in High Middle Age units are 6 trebuchets and two crossbows.
the best defensive units are 4 knights and 4 trebuchets.
To check the table guide for military building and units please click me: http://forum.en.forgeofempires.com/s...ll=1#post40293
P.S.: please note that all the above are only my personal opinion and I have the opportunity to win three times continuously in HMA PVP battle among my neighborhood including the current one. This advise is not final. Attack and defense in the PVP tournaments are always depends upon the terrain and the enemy army. so better to keep a look at the enemy military buildings before you plan an attack.