So you want to shrink images with PHP and ImageMagick. Here are samples of all filters so you can select the one you like most.
Near every image, there's an average time spent to make this picture. And there's an easy way to compare two neighboring filters - just hit one "show/hide" checkbox several times in a row.
In case you want to make the same test with any image - here's a tiny app to resize any image to any width with every filter.
Show/Hide filters
scaleImage 8.8ms


FILTER_POINT 9.3ms


FILTER_BOX 8.6ms


FILTER_TRIANGLE 11.8ms


FILTER_HERMITE 12.2ms


FILTER_HANNING 39.9ms


FILTER_HAMMING 38.4ms


FILTER_BLACKMAN 31.6ms


FILTER_GAUSSIAN 27.3ms


FILTER_QUADRATIC 14.5ms


FILTER_CUBIC 26ms


FILTER_CATROM 19.7ms


FILTER_MITCHELL 22.4ms


FILTER_BESSEL 27.9ms


FILTER_SINC 29.2ms


FILTER_LANCZOS 26.4ms


scaleImage 9.2ms


FILTER_POINT 8.8ms


FILTER_BOX 6.3ms


FILTER_TRIANGLE 10.9ms


FILTER_HERMITE 11.4ms


FILTER_HANNING 25.3ms


FILTER_HAMMING 36.9ms


FILTER_BLACKMAN 35.6ms


FILTER_GAUSSIAN 36.6ms


FILTER_QUADRATIC 28.9ms


FILTER_CUBIC 28ms


FILTER_CATROM 34.2ms


FILTER_MITCHELL 29.6ms


FILTER_BESSEL 40ms


FILTER_SINC 39.5ms


FILTER_LANCZOS 29.6ms


scaleImage 12.5ms


FILTER_POINT 21.4ms


FILTER_BOX 23.6ms


FILTER_TRIANGLE 22.2ms


FILTER_HERMITE 32.1ms


FILTER_HANNING 43.3ms


FILTER_HAMMING 45.2ms


FILTER_BLACKMAN 41.8ms


FILTER_GAUSSIAN 30.2ms


FILTER_QUADRATIC 27.7ms


FILTER_CUBIC 32.1ms


FILTER_CATROM 16.3ms


FILTER_MITCHELL 14.7ms


FILTER_BESSEL 15ms


FILTER_SINC 16.4ms


FILTER_LANCZOS 10.8ms


scaleImage 8.8ms


FILTER_POINT 8.8ms


FILTER_BOX 4.8ms


FILTER_TRIANGLE 7.5ms


FILTER_HERMITE 11.4ms


FILTER_HANNING 16.6ms


FILTER_HAMMING 16.6ms


FILTER_BLACKMAN 12.8ms


FILTER_GAUSSIAN 10.3ms


FILTER_QUADRATIC 6.6ms


FILTER_CUBIC 6.9ms


FILTER_CATROM 8.4ms


FILTER_MITCHELL 14.2ms


FILTER_BESSEL 9.8ms


FILTER_SINC 12.6ms


FILTER_LANCZOS 10.4ms


Looks like FILTER_SINC creates best images.