@Otaku It's difficult, if not impossible, to be objective about pack ratios, but I'll try my best. Due to holo basic energy, Call of Legends are by far the most valuable, worth a whopping 5 to 8 FLF packs depending on who you ask. Honestly, not that many people are willing to trade CL, so good luck if that's your thing. I have seen other HGSS packs trade at a fairly high value as well, but I can't be certain on their value at the moment. After that, Plasma Freeze is the next best, because SR Ultra Ball goes for 60+ packs. Next is Plasma Blast, probably for the reasons you stated. Emerging Powers and Legendary Treasures are by far the worst, commonly valued at 1/3 or 1/2 of a pack. XY is in low demand, but definitely worth more than LTR & EPO. Beyond that they're all fairly even, although you can bet your bottom dollar Boundaries Crossed is going to be big due to FA Landorus EX. I have a soft spot for Dark Explorers as well.
The ZaftCo thread on the official Pokemon TCG forums (in the trading section) attempts to put a more precise value on pack conversion, but if you blindly follow those conversion rates you'll get burned sooner or later. Follow your intuition, because you may see something coming before they update the conversion rates. For example, I am very confident that BCR will increase in value, if it hasn't already. Their thread still lists BCR as equal value to packs such as Plasma Storm, which doesn't seem right to me.
As for a trading thread on 6P, I find it to be extraneous. IMO posting your own public trades is by far the best way to get good deals, but takes the most patience. Lots of people check public trades every day, and it is a much more direct way of trading than trying to organize trades through the forums. I don't even bother with private trades in game anymore. I find them to be too time consuming, and full of rude traders and serious lowballers.
If organizing trades on a forum is more intuitive for you check out Top Cut Inc. and ZaftCo on the official Pokemon TCG forums. Expect to pay the absolute highest fair price if you go through them. Alternatively, you could create your own trading thread on those forums. You would get a lot more traffic from traders than you would here.