I use Ministry of Rock, RealStrat, RealLPC, and RealGuitar, along with Amplitube 3, and can generally get a MIDI track that doesn't make me cringe (from a MIDI track level of expectation).
Guitar is tough to model. Always has been. I listened to hours and hours of samples, and did a lot of reading of forums and watching of videos before I decided which samples and plugs to buy. In the end, the choice came down to more or better. I chose better, and I think you should too. You've tried what you already have and you're still looking.
Line up multiple tabs with audio or video snippets. Come up to higher than normal levels and A/B/C your options. If cost makes you gunshy, play what you're using now and think on how long you're going to be hearing that before you get where you want to be on a fretboard.
One advantage of the samples thru amps is avoiding tweak time. The disadvantage is that most of the sounds are known, and in some cases, dated by familiarity. Don't just listen to manufacturer's snippets, go on Youtube and find independence. Naturally, check the video specs so you can compare apples to apples. 480 or better, 720 if possible,.