Vanguards - Ice or fire?

It can certainly be a lot of fun. Give your team members Squad Cryo Ammo, and use Inferno yourself. Charge in on an ice effected enemy and then if needed fire your shotgun with Inferno Ammo.   (I do not know how well that works on the highest difficulty though.)

In Mass Effect 2, for a charge-heavy Vanguard, the general consensus is that you take Incendiary Ammo (Inferno Ammo evolution) and Squad Cryo Ammo for the squad. Inferno Ammo can panic organic enemies in a radius if it panics the target organic you are shooting. Squad Cryo Ammo is good for the squad as it gives them a chance to freeze enemies for crowd control. Cryo Ammo is good against synthetics since they will not panic when set on fire.

In Mass Effect 3, Incendiary Ammo with rank 6 Explosive Burst. Rank 4 squad bonus if you want to give it to your squad. Mainly you want to prime/detonate fire explosions and biotic explosions as a Vanguard.

Squad Cryo is aces for Vanguards, especially in 3.
Charging into a chilled/frozen enemy then blasting with an Explosive-Burst upgraded shotgun never gets old.

It's worth pointing out that Inferno/Explosive-Burst essentially turns every single weapon you put it on into a mini grenade launcher.

Though there's something to be said for inverting that and going for what's called a "Cryoguard"

It relies more on SMGs rather than pistols to maximize C.A. chances of freezing, but there's nothing stopping you from squadding out I.A. to give your team extra firepower.

Basically the two most common Vanguard builds:

Charge-focused Vanguard:
4 - Inferno Ammo
4 - Squad Cryo Ammo
4 - Heavy Charge
4 - Improved Shockwave
0 - Pull
4 - Destroyer/Champion
1 - Slam

Balanced Vanguard:
4 - Inferno Ammo
0 - Cryo Ammo
4 - Heavy Charge
4 - Improved Shockwave
4 - Pull Field
4 - Champion
1 - Stasis*

* Stasis cannot currently be unlocked by conventional methods in the Legendary Edition. (It is supposed to unlock as an available bonus power after completing Lair of the Shadow Broker for the first time). Slam is a good substitute.

If you are a charge-focused build, anything outside of charge and ammo powers is mostly ignored. Slam is decent if you want a one-point wonder to set up Warp explosions with Miranda/Thane/Liara. Shockwave is useless on a charge-heavy build since you would rather spend your cool down on charge than Shockwave (both 6-second base cool downs).

If you are more of balanced Vanguard that uses more powers, then Cryo Ammo interferes with Pull, and Shockwave cannot hit frozen enemies for some reason, so you ignore cryo ammo. You will still charge, but you use in combination with your other biotic powers.