I don't like spin offs much. I play Colosseum and XD, and the N64 spin offs. But I'm not fond of most of the handheld ones. PMD is okay if you're in the mood for it, I hate Ranger with a passion, and the others aren't worth mentioning. Nobunaga's Ambition actually looks pretty decent though.
I wouldn't put spin offs on par with any main games, though. They're a breed all their own, and honestly can't compare to even other spin offs, because they're just all so different from each other. Story wise, which is comparable to main games, excels more than the main games typically I think (PMD, Colo, Nobunaga). I think Colosseum has a better plot than all the main games.