The [Exalted Blade] is [Excalibur]'s 4th ability and although slightly outdated in terms of raw damage output it still packs more than enough of a punch to kill anything DE considers content and beyond.

Core Mods:

[Condition Overload]: Works on waves providing a massive boost to raw damage. Use a dedicated primer or companion primer to get the most out of this mod.
[Sacrificial Steel]: Considering all acolyte mods, including [Blood Rush] cannot be equipped on exalted weapons you're forced to use [Sacrificial Steel].
[Organ Shatter] and [Gladiator Might]: The standard crit damage mods.
[Berserker Fury]: Even after several nerfs the mod is still a stable of most builds.

Grineer (Chromatic):

Last Slots: [Primed Smite Grineer], [Voltaic Strike], [Primed Fever Strike].
Chromatic element: Heat.
Explanation: Grineer units are heavily armoured. If you can't ignore said armour your second best approach to dealing with them is stripping some of it with corrosive and heat procs.

Corpus:

Last Slots: [Primed Smite Corpus], [Virulent Scourge], [Primed Fever Strike].
Chromatic element: Toxin.
Explanation: Corpus units are heavily shielded. The best way to deal with them is by simply ignoring their shields with toxin procs. A pure tox [Exalted Blade] deals the highest amount of toxin damage.

Infested:

Last Slots: [Primed Smite Infested], [Voltaic Strike], [Primed Fever Strike].
Chromatic element: Heat.
Explanation: Infested units are pushovers. The only units that will put up a fight are the ancients and deimos units and they are weak to corrosive, innate heat's there for the bonus damage and armour strip.

Corrupted:

Last Slots: [Primed Smite Corrupted], [Voltaic Strike], [Primed Fever Strike].
Chromatic element: Heat.
Explanation: Corrupted units are a mix of units from other factions. Ideally you'd want to bring different elements to deal with each type but because that's impossible your best bet is to build for their heaviest units. Those units are the corrupted grineer units so you're basically just building for grineer with a corrupted smite mod and just like in the grineer build since you can't ignore their armour your second best approach to dealing with them is stripping some of it with corrosive and heat procs.

Sentients:

Last Slots: [Virulent Scourge], [Primed Fever Strike], [Sacrificial Pressure].
Chromatic element: Heat.
Explanation: As of update 30.7.2 sentients are vulnerable to status effects. As there's currently no Smite mods specifically for sentients the next best thing is to use the set bonus of the Sacrificial mods instead. As this build requires two sacrificial mods to be used going for it on [Excalibur Umbra] is preferable to normal [Excalibur] as you don't need to spend the umbral forma needed to fit this build.

Other, less important builds:

Grineer (No Augment):

Last Slots: [Primed Smite Grineer], [Melee Prowess], Carnis Mandable.

Explanation: Grineer units are heavily armoured. The best way around this is ignoring armour with slash procs. I do not recommend this build though as the full build only has about 33% chance to actually proc slash, meaning two thirds of your attacks will not do any damage. With that being said, unless you want to fullstrip this is the only way to play [Excalibur] in endless missions. For standard steel path and below, DO NOT use this.

Grouping Build:

Last Slots: Mission appropriate Primed Smite mod, Voltic Strike, [Shocking Touch]
Chromatic element: Electric.
Explanation: If you have the ability to gather up (and or strip) enemies than a build like this will make swift work out of the grouped enemies. Just keep in mind to not ragdoll enemies as that screws with electric proc hitboxes.

Notes:

[Gladiator Might] is used extensively because I expect you to be using a combo stick gunblade to get consistent crits on the frame.

Alternatives:
[Quickening] can be used instead of [Gladiator Might] if you have no external way to buff your attackspeed and are not using the aforementioned method of boosting your crit chance through gladiator mods.
Primed mods: Use non primed versions.

Q&A:

Q0: Do you have a good [Excalibur] build I can use this with?
A0: Absolutely.

If you have any other questions feel free to ask.