AGS is in exactly the same boat as PTS. If you own AGS on Feb 28, you get a share of BTS. If you buy AGS after Feb 28, you won't get BTS for it, but you will still get a share of all future DACs. Thus, it's likely that AGS (and PTS) will be cheaper after Feb 28 than it is now, because right now it has the value of BTS built into it. There's no way to predict how much cheaper it will be.
Of course you'll still be able to donate to AGS after Feb 28, because BTS isn't the only DAC that Invictus plans to launch.
The question of "better" is impossible to answer right now because we don't know the market prices of PTS or AGS post-Feb 28.