Both T25 variants are pretty awesome. IMHO, the T25 AT is the most fun you can have in the US TD tree. But ultimately, it depends on which line you want to end up with.
The 25/2 line lets you branch over to the fixed-gun line at tier 8. The turret line is noticeably faster in tier 9-10, but more vulnerable to fire. The fixed-gun line is slower, but can hold a choke point solo and often requires arty intervention to defeat.
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'92 Suzuki GS500E (sold)