best for u to go for android. HTC HD used older winmo 6.5 which is not really great. why not try HTC desire which used better android platform there? windows7 phone also still lack of support to our country, such as no market for Malaysia currently..
u want customization? avoid iOS.. with your budget, u can get AP HTC desire. or AP motorola milestone (if u want keyboard, and the screen is larger to desire by 0.2", sacrificing processor power a bit)
bettr top up a bit, get AP SE X10 for nicer cam. u can get LG optimus one for less than 1000. but the cam is so-so..

SE Hazel. but need topup a bit. if lucky, can find SE W705 around.
both did not support web flash and of course X8 IMO better than X10 mini, except for their camera, X10 mini did outperform X8. but did suggest u to topup just a bit, can get super smartphone X10 8mp+HD record, 4", 1Ghz. in anyway did better than both X8 and X10mini.

I use android 2.1 Stable la. 

it is ok. but since u want wifi b4 in the preferences... I only not favoured SE phones for the fastport only.. if and only if it got 3.5mm...   (since it is newer slider, can expect it to last longer than previous maybe..)
all u mentioned b4, X8, X10mini, all used android. and of course, stable. if u favoured more, there are lots to looks for (custom ROMs etc. well, u know, android )

The colour, the reproduction. The resolution.
It's like comparing between a CRT monitor and an LCD monitor.

IMO,

my preference:

Retina Display > SuperAMOLED > SLCD> TFT >LCD

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Added on February 15, 2011, 12:24 am

CSL Mi300, don't let the name fool you. Solid phone for it's price
LG Optimus One would be a better choice. Gimme budget, and i'll see what i can do.
Xperia x10 if you take pics alot. if up by 0.4k, can get nicer phones.