StB/DS... no. Just no.
The Last Spell system in IN is really nice; I feel really great even seeing that Last Spell, since I feel like I earned it; if I cap it, all the better. However, I can't vote IN in good conscience since goddammit, I will focus or unfocus wherever the hell I feel like it, and no scoring incentive can change that. Implementing the youkai/human gauge as a damage bonus or something would have been better, but still a little forced.
SA is out since it promotes bombing and suiciding for graze. (Blech.)
MoF is fairly solid, but it doesn't punish bombing enough, and dying, too harshly. Also, PoCing at the wrong times can really put a dent your Faith meter, which just feels... wrong.
PCB, UFO, and TD are my finalists, because they balance survival vs. scoring well. This inherently rewards good play, since the less you have to worry about survival, the more you can pursue score simply by virute of not needing the extra resources that would otherwise require you to sacrifice scoring potential to get. Borders can be used as a free bomb, or to increase your score multiplier, but not both. Unfortunately, timing your borders involves metering your focus status and drop collection, both things I've already expressed concerns over.
UFO, you can get hellabuncha resources by building red and green UFOs, but serious score runs demand rainbow and blue UFOs instead. However, lack of ability to summon UFOs during a boss kinda takes some of the focus away from the main event, so to speak, and I'd like to see a bit more reward for not screwing up spellcards (something that IN did very well).
TD... is amazing in nearly every aspect. You have to choose between using your trances to multiply your resource intake, or during gluts of white spirits for massive multipliers. Simply gathering enough spirits for a trance to begin with encourages agressive play. Unlike UFO, the gimmick is still in play during boss fights, and capping spell cards gives you a bonus of extra spirits. Now, it's not perfect, since the "automatically use up all your trance gauge when you die" thing means one poorly timed mistake can screw you up a bunch, but all in all, it's a very impressive system, and I hope to see more like it in the future.