Ya know the answer already....... you already eliminated the SKS in your first 13 words....... if you want a rifle that
LOOKS like an Assault rifle,
FUNCTIONS like an assault rifle in semi auto mode And
FEELS like an assault rifle then you have already cut your choices down to either the AK or the AR since the SKS has absolutally none of those characteristics unless you throw a bunch of worthless plastic wannabe an AK cr@p on it and even then it still will not fit the bill and you will have thrown a bunch of $$ away and still will need to buy your "Assault rifle"
Now that we have narrowed that down to either an AK or an AR, I'll ask how much do ya like having to tinker and tweak your guns to get them to function reliably? Because unless your an experienced smith this rules out those kits listed above as in 20+ years of smithing primarily military battle rifles that is always the case of the kit built AR........ if you like to tinker, enjoy replacing inferior mime parts as they go outa spec etc... then a Kit AR is your choice...... for $600 your not going to get a quality AR, like they say ya get what ya pay for and when it comes to budget ARs that means cut corners and low quality components to resemble an actual semi reliable battle rifle....
Now if ya wanna drop your new "Assault rifle" outa its box, load up a mag and go shooting with zero problems, all first rate Milspec components etc.. then spend $499 for a Lancaster basic AK via Atlanic arms If you can buy in person and don't mind a finish thats a lil lower grade than the Lancaster Moly resin over park go with a Yugo M70AB1 or M70AB2 the finish is just parked which has served militarys well for 60 years but still not a moly resin over park finish However you will get a heavier receiver, built in tritium night sights and many othe features still all milspec components, if ya gotta buy sight unseen then ONLY order from Classic arms as they actually inspect their Century distributed guns before they ship them the Yugo will run ya $429 right now, and if ya go for the underfolder and want to replace the black plastic forend that will run ya another $69 or so bucks for exotic wood.
Now for a few bucks more ya can get that Lancaster AK configured as an M4/AK with alluminum 4 rail front end, collapsable stock, you can add a side scope mount yourself in about 5 minutes and a $34 rail using button head allen screws, you will need to be capable of drilling two 3/16" holes.......
Classic arms
http://www.classicarms.us/
Lancaster built Romanian "G" milspec rifle at Atlantic firearms Basic version
http://www.atlanticfirearms.com/programming/expand.asp?Prodid=275
Lancaster built Romanian "G" milspec rifle at Atlantic firearms M4/AK version
http://www.atlanticfirearms.com/programming/expand.asp?Prodid=276
Either is well worth the extra $$ over a WASR or STG2000 (both are non milspec components and both built in the same factory for different distributers the WASR is Century the STG2000 is Interordinance internally etc.. they are the same gun with cosmetic differences)
My personal favorite are the Yugo M70AB2s but all of my AKs (over 400) are built by me over the last 20 years. Before my recent divorce we used to host shoots out at our place every weekend, usually between 40-50 people and while there were always several ARs, SKSs, FALs, CETMEs and G3s set out the AK based rifles were the ones everyone shot the most and the ones everyone visibly had the most fun playing with and I don't have any bargain basement ARs, all Colt and not one of em is prone to the usual jamming or other failures ya hear so much bout... but folks just never got as excited as they did playing with the AKs, most guys would gravitate to the L1A1s and other FAL patterns but after only a few rounds they'd put it down and go checkout the table of AKs, many never even fired the ARs and if they did it was only a mag or two and....... over to the AK table
Ammo right now for the AK will run you $189 per 1000 round case delivered to your door in bout 5 days
http://ammoman.com/index.htm
this is the page ya get if ya select 7.62x39 from the above
http://ammoman.com/webstore_762x39.htm
Military gun supply, has a pretty good deal on a polish underfolder,
$595 For Polish underfolder at Military gun supply
http://www.militarygunsupply.com/shop2/index.php?main_page=product_info&cPath=14_16&products_id=215
however of all of the AK builders only Lancaster arms offers a lifetime warranty, Colt doesn't even have that much confidence in the AR15s they sell me!
good luck with your selection