it's sort of difficult to compare the two because TERA is hitbox-based and BDO is invisible-targeting-based
basically, in TERA, attacks create an area or field that then affects what it touches, like an arrow becomes a little hitbox that sails across and deals damage if it hits the target
in BDO, attacks are scripts that are run on a target or an area, which then affect anything in that area. this means that when you fire an arrow the target is already "hit", they can't dodge or whatever, which his why this game has "accuracy" and "evasion" stats unlike a real action game
so obviously this makes TERA better right? well…
1) that's a matter of preference
2) the combat in BDO can be much faster as a result
3) each character class has many more moves in BDO than in TERA, and you activate them wtih direction+attack key combos rather than pressing 1, 2, 3, etc
there are other upsides to each game; TERA has (mostly) non-gender or race-locked classes while BDO has charagen somewhat like Mabinogi Heroes (vindictus for amerifags) or other korean games, your character isn't a set person with a name and stuff, but, a "Ninja" is always a human dude, a "Dark Knight" is always an elf girl, a "Berserker" is always a male giant, etc… although I will say that customization is pretty good so two characters of the same class can look pretty different
BDO has a lot more to it outside of the combat, also; the lifeskills system is pretty well-developed (like ArcheAge-lite) while TERA's crafting is, uhh, not – BDO also has an inter-settlement trading system, an Amity system where you can make NPCs like you, a whole mount leveling/training/management system with breeding, and so on
I played TERA for about a year and I enjoyed it during that time but after playing BDO and a few other newer games it just kinda feels dated
