Your stated criteria is speed and reliability, so it has to be the Xeon with SSDs. You probably won't squeeze as many accounts into it as the others (depending on i/o load) but they are more likely to still be up in 12 months.
Have a look at hardware RAID options also, if your budget stretches, and also do some background digging on the OCZ drives - some SSDs have less than stellar reputations and I can't remember where the OCZ drives sit.
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If speed an reliability is the main factor, go with the E3 (#2) hands down. ECC ram will be used which from many years of first hand experienced, makes a world of a difference when running servers coupled with SSD drives, you cant go wrong. 16GB ram for the most part is plenty too.