You may want to consider selling the rigs you have and looking for a Kenwood TMD700 or D710. That way, you will only need one antenna for APRS, and the muting of the second receiver is handled for you in advance.
To some extent, your antenna will affect your performance. If you're close to an iGate most of the time, it probably isn't critical at all. If you're operating on the fringes, you may want something bigger.
EchoLink, IRLP, Allstar and DSTAR linking - adding interest to repeaters worldwide 24X7