Well everyone is going to have differing opinions, but there is a lot to be taken from everyone here.
My opinion of course.
I have a sp505, st-224, and mpc500. I also use FL Studio with lo-fi plugins.
My favorite vst is "time machine" it's free btw, and do great aliasing effects.
As for the hardware samplers......The 3 I have are all good in their own way, and all have limitations.
The mpc500 has the most features, and believe it or not due to re-sampling it can sound dirty, I mean sp12, or sp303 dirty!
You just gotta know how to freak it. The 500 has an over complicated file management system though, and this is it's downfall until you figure the dang thing out.
The 505 has the best file management since it auto-saves everything. this is only a problem when you delete something you didn't want to.delete. The effects being boss sp fx are arguably the best of the 3 also. Everyone loves them some vinyl sim!
The st224 is not to be dismissed however. It probably does the best job of emulating an sp1200 of the 3.
Just like the sp12 the sound degrades, and aliases when you de-tune, and just like the sp1200 it has a 24ppqn sequencer.
So you get a very funky swing when recording at double bpm.(No song mode though same kind of sequencer as the 303 where the pattern switches as soon as you trigger it).
The low pass filter is also the best of the lot, and the compressor has character.
They are all cheap to buy. the 500 has the best build quality, and the 505 the worst. The 224 has decent build quality too, but not like the 500.