I don't build ships below 10kt ( usually go in 10kt steps ) with 20-30kt most popular size for early to mid game
higher tonnage means I can easily put 2 or 3 weapon systems as loss of efficiency on higher tonnage is not significant
My fleet can be most often locked into 2-3 types of ships which I can refit if needed and which are all around ships
beams +gauss for 10/20kt and beam + gauss +box launchers for 30/40kt and bigger
knocking any ship out of the line in battle doesn't make any hole in combat capabilities (sensor/offence/PD)- only percentage overall reduction
it is cheaper in the long run , easier in refits , easier with managing shipyards , and finally I don't loose many ships this way (smaller ships are really very fragile)