libor vs. 12 mta - which for your ARM?

libor vs. 12 mta  - which for your ARM? -- assuming we'll be
moving/selling by August of '05, so we only expect 21 months.

Assuming CAPS and prepays and points were the same, and the MARGINs
were different, but worked out to be about the same Index'd rate,
please tell me why would you pick one index over the other for your
short term ARM?

thanks.

(note, I see the 12 MTA at 1.22 + my quoted margin of 2.4, so indexed
rate of 3.6; i see the 6 month Libor at 1.22 + my quoted margin of
2.28 for an index'd rate of 3.5%)