I like your choices in potential boats. I'm not an impartial judge though since I own a T27.
We race our T27 against a T30 and often enough we get 1st place after PHRF correction. That said, not all T30's are the same. There is a tall mast version and a standard version and the boat we race against is the std. version.
"The standard rig includes a fin keel with skeg hung rudder that draws 5' while the tall rig has an extra 3 feet of mast, 5'6" of draft and an extra 500 pounds of lead."
Source: TARTAN 30 sailboat specifications and details on sailboatdata.com
The T27 has a modified full keel that is 3'6" deep. I've heard it referred to as a full keel with a cutaway fore foot. This helps it track well on a course. It also makes it a bit slower to come about. The center board drops to 6' and allows one to move the CLR fore or aft which you can't do with a big fin keel like the T30 has.
The T30 would be my choice if I was looking for a 30' boat. The engine access on the T30 is wonderful. I'd bet that the cabin interior seems twice the size of my T27.
Perhaps for obvious reasons I like the look of the T27 better then the T30. The T27 sails wonderfully even with the center board all the way up. The shallower draft is nice for coastal cruising and being able to get into skinny water places.