Trilogy includes the three “campaigns” which are stand-alone games: Prophecies (i.e. Vanilla GW), Factions, and Nightfall. You can get any one of those and play to completion.
GotY includes Prophecies only (so you can play it all the way through) and some starter items, including the igneous summoning stone — that last one is worth a few bucks alone for the convenience during level up (it is a free summons that you can use until max level).
Eye of the North is the only expansion (in the sense of requiring a base game). You can only play it if you own Proph, Fact, or NF. It is also the bit you need to link your accounts, as it provides access to the Hall of Monuments and the relevant GW2 rewards.
If money isn’t an object, I’d get Trilogy + “Platinum” (if steam offers it — it’s Proph + GotY + EotN). That gets you everything, plus some convenience items.
If you only want to link accounts and get some HoM rewards, I’d find a package with any one of the stand-alones + HotN. Factions is considered to be the shortest campaign, Prophecies the longest with extra skins suitable for the HoM, and Nightfall includes extra heroes, which help when you can’t find others to team with.
PS you can find more information about the various GW products on the GW1 wiki, e.g.
http://wiki.guildwars.com/wiki/Guild_Wars:_Game_of_the_Year_Edition
John Smith: “you should kill monsters, because killing monsters is awesome.”
