Yeah, assuming you mean a metal post and metal frame I'd use the white grease. Just enough to make a thin coat. The purpose isn't so much in aiding the insertion of the seat post but to prevent corrosion or galling that makes removal difficult or impossible, so you want something thick that will stick around for a while. The tri-flow and ultra-lite oil are way too thin and I've never heard of TriGEL but I've successfully used white grease many times for this purpose.
I don't think grease matters, yet alone what type. Most people make it without using any grease at all. I've never had a problem with stuck seat post. I think they added some grease 4 years ago when I bought the bike. I've had it out several times since and never regreased even though I have grease. No reason to use when not needed.
I think I would go with the creamy type substance. If you have both and try the creamy type substance and are not happy with it. Perhaps you should attempt to try the other one. You might prefer the oily one over they other.