Both sliver boxes and the base has their downside
Not a lot of people liked when the base update come around due being like most building city mobile games like clash of clans note:clash of clans isn't really bad mobile game
The sliver box were like the daily boxes but costs a little coins also having chance of epic items
Downside is really big but as stefix5000 said
The base:is like mobile games: 1st upgrade 2nd wait 3rd comeback 4th upgrade 5th wait you get the idea
It gives free coins thorough the gold miners
The factory kinda suck especially the chance of epic item card but it takes forever so it's not worth like cheap but slow item production but some cards are great best example is power kits which is great for boosting items because power kits are hard to obtain from boxes
The downside for the base is basically this (1st upgrade 2nd wait 3rd comeback 4th upgrade 5th wait) you can't really upgrade anything you without the other upgrading the base to lv15 will take month my base is currently level 13 today i upgrade it to level 14 but it will take 3 days to be finished the gold miners all are lv13 and 1 lv13 factory and the others are 10 and 4.
Its up to you to decide what you prefer