Great choices, but Resistance is likely to get used much less often than Guidance. It's hard to know in advance when a saving throw is coming.
Guidance is awesome, but it's actually least awesome for warlocks, because it needs concentration. Warlocks have a concentration spell, Hex, that they (sometimes) keep up all day, even between combats, and even use in town on non-fighting days. Yes, you already lose hex whenever you cast a ritual. And yes, other classes use concentration too. But they tend to let it go at the end of each combat. It's something to consider.
The best choice largely depends on what group you're in. If several others in your group already have a certain cantrip (Spare the Dying, Guidance, Message, Mending, Thorn Whip, etc) then there's less need for you to get it; just let them use it. For instance, if three people all cast Vicious Mockery, the target still only gets disadvantage once.
Personally, I love Mending... since it's a touch spell, you can even cast it through your familiar (which you get through a ritual). For instance, to safely repair the tiles, or a flag, on the roof of a tall tower without having to climb it. Actually, many cantrips can be cast through the familiar: Guidance, Light, Magic Stone, Mending, Resistance, Shocking Grasp, Spare the Dying.
Small note: If you multiclass to cleric/druid/wizard, be sure to get utility cantrips from multiclassing (they'll use wis/int), and any attack cantrips through the tome (they'll use cha).
In combat you're all about Eldritch Blast. But there are three reasons to consider other attack cantrips. 1) Sometimes your target has a really high AC (either from armor or cover or the Shield spell), so you're better off using a cantrip that uses saving throws. 2) Sometimes your target is knocked prone (usually by the fighter-types in your own group) so you have disadvantage with EB. 3) Sometimes an enemy is standing next to you so you have disadvantage with EB.
Condition 3 isn't so bad if you have good AC (from multiclassing or the Moderately Armored feat). EB is practically the only ranged-attack spell you have (Ray of Enfeeblement, which sucks, the first round of Witch Bolt, and possibly Scorching Ray if you chose fiend), so enemies standing next to you isn't always a big deal. But even then, EB is so good that it can still be a good idea to move away from that enemy, just so you can resume casting EB without disadvantage. Shocking Grasp and Minor Illusion are the only cantrips that really help you move away from an enemy. Ok, but sometimes you don't care about moving away, as I mentioned. EB with disadvantage is sometimes still better than something else. Well, if your target has medium or heavy armor, Shocking Grasp also gets advantage. It can be hard to accept disad when you could have advantage instead.
Condition 2 happens rarely with some groups, constantly in others. How often in your group? Even worse, sometimes the fighter just stands there after knocking him down, so your target _also_ has cover from the fighter. Shocking Grasp works if you're willing to move up, and even gets advantage, but a cantrip that uses saving throws instead of an attack also works. However, a saving-throw cantrip doesn't get the extra damage from Hex, and also can't get critical hits, and also usually won't get advantage. Critical hits might seem rare, but if you use Hold Person often, you'll definitely want to critical-hit your victims every single round.
Condition 1 is a bigger problem for melee types than for you. Just use your spells. Or suck it up and use EB anyway. But if you really want to save the day when disadvantage, cover, and high AC all converge, one more fighting-cantrip is acceptable. If your target has low Wis saves, you already have many choices (hold, charm, fear, dominate, hypnotize), so Vicious Mockery is probably best left to other casters. There are a whole bunch of options (only Poison Spray in the Player's Handbook, but more from other sources) which are already on the warlock's cantrip list. The only two that aren't are Acid Splash and Sacred Flame. Sacred Flame is my favorite, because of long range and good damage type and can't-miss against paralyzed/petrified/stunned/unconscious, but really any of them will do.
