well, i've heard people rave about all of those so it's hard. massey demo's can be used with a minor limit and it's rtas (some au's too),
colortone and nebula use impulse type capturing of gear from tape, console, eq, etc even samplers many say nebula has the best emu but it's a cpu hog and can be wonky, colortone is wicked and i use it all the time, same as the ac 1 and 2 when i'm in pt
many also love urs saturation, i remember terry hogarth raving about it.
psp and magix amsuite are highly underrated but also get a shitload of praise
duy, virsyn and cranesong have been considered the best at some point and for some, still are.
honestly, i would lean to colortone pro, psp, amsuite or nebula not only due to price but also for all the other things they emulate, huge library/presets included, commercial and user based and the option to make your own from your gear. the only caveat, is the wonkiness, i already mentioned nebula's but for colortone pro it needs pluggo runtime but it comes in rtas as well as vst.
dream already stated his love for reeltape (it's not a digirack plug but it is digi's like smack), and though nomad has greatly improved their plugs, back when people were dismissing them they would still admit that nomad was good at valve and tube effects.
try to get some demo's (virsyn will be a prob it uses a different dongle than ilok, the same one as cubase and korg) and get the free ferox and massey tapehead (and their other stuff)