Having just returned from the schoolhouse, both posts are correct.
As I was told by an Instructor, initial is based on the -300 with a
-700 differences day.
If you bid and are awarded HOU or DAL, you will be given -200 training.
99% of the pilots currently on SWA's seniority list have flown the -200. Comments concerning the merits of the aircraft in today's environment vary widely.
The -200's retirement began with a geographic consolidation program, hence the HOU and DAL base restrictions. Eventually, the -200 will be phased out ( I think we have 24 +-2 of them still flying); with the -300 comprising the bulk of our fleet for a short time. If the 'rumored firm orders' materialize, it won't be too long until the -700 is the dominant type.
A side note; the -300s are being readied for a glass cockpit (different than the current -700) conversion with the -700s scheduled shortly thereafter. The demo slides we were shown are impressive, specifically a display of our position on the 10-9 Jepp page.