Gosh... I hate 1.3. With a passion. I like the increased map size capability, but I just can't stand the brush and vertex selection in it. At least in 1.5 it's much more intuitive, which is why I use both.
I've always used 1.5, shunning the lack of texture panels and easy navigation in the other versions. Sometimes I go 1.6 if I want to corrupt my map, use the handy brush split vertex tool and crash the program. Just tell me which version will texture end caps correctly going nuts
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