This has been a topic of debate with myself really and I can imagine with most of the rest of you.
On the surface I immediately went straight to Immortals being that they had a better save....Then I thought how cheap the Warriors are, I can take say 30 of them for a mere 390 points. That is pretty impressive. That is not to say you will take 30 but I would for that cheap haha. The thing that makes them more tempting is they have Gauss which you can auto glance on a 6, if you bring 30, very tasty. And I think if this is coupled with a couple of big units of Scarabs, obviously one of the stars of the Codex, I think those shots could get scary. Very scary. This is just one case for them. There is also the case for bringing a Ghost Ark. What has surprised me is the lack of use this seems to get in peoples lists. Especially when they are running Warrior units. It's open topped so can be fired from, AV13 protection and if you disembark or if you have a unit nearby on a roll of a 2+ you get D3 Warriors back from the dead. That could be objective sitting to the max while keeping those lovely Gauss shots. That being said I also think they benefit from large squads. I think the thing I find most funny is how people have been putting up lists with small 5 man Warrior squads, that will not last long. I won't go any further with these but I will say I like the look of having a couple of big units of these guys and maybe one unit of....
Immortals, coming in at 17pts per model with a 3+ save and with a Gauss Blaster rather than the Warriors Flayer with a point increase in Strength and AP bringing it to S5 AP4. Or and this is the part I like, exchange those to Tesla Carbines with that lovely ability of a roll of a 6 for two hits. The AP - hurts it but I think this is fair due to it could get rather nasty. Overall I think these would do nicely for thinning out infantry. A unit of 10 with these could be nasty. You don't need to go Tank Hunting with these as you more than likely have a bunch of Scarabs munching to give the rest of your armies weaponry good chance of destroying everything. I think a unit of 10 Tesla Carbines coming in at 170 is a good deal. If you want to make them your main troops I think Night Scythes (when they are eventually released) will be brilliant. I would recommend possibly having one 10 man unit with a few 5 man units dependant on points level if these are your main troops.
Personally I like the idea of mixing them but it seems alot of 'net lists' have made the Immortals the only logical choice. I think a good idea would be to have two big groups of Warriors backed up by small groups of Immortals with Tesla say for example you have 20 warriors back them up with two 5 man Immortal Squads.comes in at 430 points. This is just for an example and I'm not saying that's what you should run exactly but you get the idea. I personally think that the Ghost Arks maybe getting sold short a little especially if your running a predominate foot list. I think they are a viable choice seen as they make your warriors even more survivable.
I don't think I have to say anything about the Night Scythe seen as most people think that's the only choice haha.
This is just my thoughts, please leave your thoughts on what you think are the best configurations for Troops are.
I shall leave you with a list I find to be the best I've written so far.