Collectors are not too bad if you have high weapon DPS, or power dps that can ignore bubble. This is because their main deal is push from Praetorians, so if you can shut down the push via DPS, the faction gets simpler. It also is a weird faction overall since it has some tough waves at the beginning, then there are coffee break waves.
In my opinion the three "easiest" setups for soloing platinum are as follows:
TGI w/ PPR 65663
You can quibble over the details of the build if you like, but the equipment and weapon setup is probably overall the best on him for a couple of reasons. You can sub in Harrier if you like on Giant, but if you go Collectors PPR is probably a little better. As far as Overload goes, I like it to strip Phantom barriers before shooting at them so I always have it. I don't find you need a second weapon if you use PPR. If you went Harrier or Lancer it would make sense to have a backup (faction dependent). There are some unusual setups that might work depending on faction (like for cheesing Cerberus), but I don't know that I necessarily recommend them for a first solo.
Batarian Soldier w/ Reegar 63656
This character is not mentioned nearly enough in the discussion of good solo characters, which is odd. I don't know if it is the lack of dodge or what. On PC this setup easily one-clips platinum Atlases (Throw Inferno Grenade, aim for Canopy triple hit section... I have done it with only Shotgun Amp II...). Also high shields, and great stagger power. If you know how to get around power block by throwing the nades at things like Banshees, they are nearly trivial as well. You have to be mindful of sync units, but as I said before Ballistic Blades is great for keeping Phantoms honest, and IG+Reegar DOT can potentially save you from Banshees.
Krogan Battlemaster w/ Reegar 60666
You can drop the HVB for Shredder if you want faster recharge, which may also mean you will take a little extra DR from Barrier, but I prefer the recharge there. I think this guy edges the flame GTS, although I haven't done a Reegar flame GTS at all. Unless you RHA the whole game (which is actually largely possible on Giant against some factions), you might need to learn about going into heavy melee for DR and to activate rage for DR. It just sort of depends on the map and faction whether or not this will be a big deal. I almost put him above the Bat Soldier, but didn't since the damage output of Batarian Soldier is much higher, and his stagger power has more range.
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I never actually tried the 0 HM + GS Acolyte GTS build, and don't intend to do so (although I have done two GTS solos - hybrid build and tank build). But out of the 27 or so I have done I recommend learning one of the 3 above. As another person said regarding the Jugg, it is not as simple as you might think just looking at the high shields. Objectives can be a big strain depending on map and what you get.