I strongly recommend against using the optional rule for flanking. It makes achieving advantage on attacks entirely too trivial, in my opinion.
My group will be starting a new campaign in a few weeks. I'm looking for ways to enrich the tactical experience (as some of the players quite enjoyed 4e).
What official variant rules have you had success in adding to the game to make 5e a little more robust?
I haven't actually tried any of these yet, but these are the ones from the DMG I would like to try, in order of decreasing interests:
1)
Action Options: These are IMHO almost a no-brainer additions if you want to increase the tactical aspect of combat encounters.
2)
Facing: Part of me is afraid that this is too fiddly, and it almost certainly requires minis to use these rules consistently. But it definitely increases the tacticalities of combat.
3)
Flanking: For some reasons, the author of the excellent The Monsters Know blog strongly suggests to use the flanking rules, while others hate them. Overall they aren't difficult to use, and they certainly
do have tactical consequences on how people play in combat. I expect flanking to generally shorten combat by increasing the average attack success rate of everyone, but let's keep in mind that this includes the monsters. Many characters/monsters might be able to use special abilities that activate on advantage more often. Then how exactly this whole thing will end up I cannot say... it's possible that overall combat even becomes
less tactical if everyone is always looking for flanking for cheap advantage and neglects every other option to get the same advantage; but it's also possible that another gaming group will start thinking harder about how to
negate the advantage of flanking monsters, thus making the whole game
more tactical. I suppose you have to try to see how it works with your players.
4)
Hitting Cover and
Cleaving are a bit too fiddly for my tastes, but are
small rules to add. The second one could actually help offsetting Flanking a little bit if it turns out that hordes of small monsters benefit too much from it.
5)
Speed Factor, honestly I would leave it last... I am somewhat fascinated by this old-style option, but in truth I do not believe that it will change a lot the
tactical choices of every player. Most martial players will still focus on their one weapon attack style they're best at and have invested into, there won't be much tactical choice on a round basis IMHO. Spellcasters might be more affected, and sometimes choose a faster lower-level spell over a slower higher-level spell, but that's it.