BMX - Help me choose a used BMX

I want to buy a BMX. With it, I want to learn to bunny hop and cruise around and have fun on it. Hopefully it would be lightweight. I am a beginner but I would like to buy a quality bike so it can have a high resale value if I decide BMX is not for me. Also my brother does flatland so I can maybe give it to him if I dont like it.
My budget is $200.
I would like a straight brake (not the gyro brakes that lets you spin the bars around), to cut down on weight; and I'm pretty sure I wont be trying any barspins.
Actually I think brakes would be optional, I can always buy some brakes later.
I would like the frame and fork to be full 4130 chromoly steel, because I read on the forums its lighter
I would like for it to be somewhat lightweight (<30lbs) and have 3-pc cranks.

Listed below are some bikes I picked out on craigslist around my area. Could you please have a look at the links and tell me which ones are worth it? I know there are a lot of links but I am new to BMX so I have no idea what to look for. My brother told me to look for companies that make exclusively BMX bikes (not also road/mtn bikes). But I noticed that Haro makes exclusively BMX bikes, but it seems some of their bikes are pretty bad, so I'm not sure if haro is a good company.

Yellow Haro BMX X-01 Backtrail Series - $150
http://orangecounty.craigslist.org/bik/1087318387.html

Red Haro Bmx bike - $200
http://orangecounty.craigslist.org/bik/1087197799.html

Rhythm BMX Bike - $175
http://orangecounty.craigslist.org/bik/1086131400.html

Free Agent BMX Race Bike - $200
http://orangecounty.craigslist.org/bik/1085823322.html

RedLine Tarmac and Trail Series - $150 (are these 1pc or 3pc cranks?)
http://orangecounty.craigslist.org/bik/1080513458.html

Giant Bmx Bike - $150
http://orangecounty.craigslist.org/bik/1078462258.html

EASTERN LOWDOWN BMX BIKE - $150
http://orangecounty.craigslist.org/bik/1076689848.html

20.75'' DK BMX Park bike - $200
http://orangecounty.craigslist.org/bik/1074138069.html

MirraCo Blend 2 BMX Bike - $20
http://orangecounty.craigslist.org/bik/1068891735.html

2008 Haro F2 20inch BMX Green - $200
http://orangecounty.craigslist.org/bik/1066891334.html

Haro F2 series bmx bike - $150
http://orangecounty.craigslist.org/bik/1065901234.html

GT FLY - $110
http://orangecounty.craigslist.org/bik/1065275012.html

Fitbike Freestyle BMX Team Edt. - $200
http://orangecounty.craigslist.org/bik/1059216692.html

Freeagent BMX bike - $170
http://orangecounty.craigslist.org/bik/1058618572.html

Custom BMX Haro/Fly/Fit - $200
http://orangecounty.craigslist.org/bik/1056060711.html

haro f3 bmx bike - $90
http://orangecounty.craigslist.org/bik/1044890385.html

Fuse BMX Model-III - $125
http://orangecounty.craigslist.org/bik/1044699956.html

dragonfly bmx biike - $150
http://sandiego.craigslist.org/csd/bik/1088578003.html

20' bmx bike mirraco.fivestarpark - $180
http://sandiego.craigslist.org/csd/bik/1084383053.html

BMX RACING BIKE MOSH EXPERT - $175
http://sandiego.craigslist.org/csd/bik/1084349413.html

GIANT GFR BMX BIKE / BICYCLE - $100
http://sandiego.craigslist.org/nsd/bik/1079176229.html

20inch Redline Bmx Bike - $80
http://losangeles.craigslist.org/lac...081739723.html

Hoffman bike - $150
http://losangeles.craigslist.org/lgb...079936442.html

mosh bmx bike - $250
http://inlandempire.craigslist.org/bik/1069775239.html

free agent hell cat - $200
http://losangeles.craigslist.org/lgb...086831385.html

dave mirra 20" $250 obo
http://orangecounty.craigslist.org/bik/1086664544.html

20" BMX Fitbike XL - $225
http://orangecounty.craigslist.org/bik/1083227298.html

BMX Intense.. - $240
http://orangecounty.craigslist.org/bik/1070236284.html

GT BMX Bike - $250
http://orangecounty.craigslist.org/bik/1055734926.html

dirt jumping bike built - $200
http://inlandempire.craigslist.org/bik/1051002150.html

Also what is the difference between a freewheel and cassette in the rear? I understand cassettes can be made smaller (9-11t) and freewheels are restricted to 15t and larger, but are cassettes better than freewheels? are they better made or last longer? From what I understand, a smaller tooth cog would wear out faster than a larger cog. But I guess with a smaller cog you can run a smaller chainring in the front and it would be less weight and size? Is that the appeal to using small cassettes?

The very last bike in that list SEEMS like the best.

Freewheels are basically a cog the threads onto a freewheel hub. They now go down to a 12T which has bushings instead of bearings. And cassettes have a driver and a cog goes onto them. A 1-piece driver can go down to an 8T and a 2-piece can go down to an 11T I think. People like them because like you said, you can run smaller gears, which in turn makes it lighter and more out of the way.

word. go with the last one.