Knott's. It has better food, better employees, better atmosphere (though admittedly it's losing it), is cheaper to get into (especially with a discount coupon--pick them up at Del Taco), more for small kids, and is a lot closer to DLR. Six Flags has really bad food (also extremely over-priced), really inept employees, is far away (with the high gas prices, that makes a difference), and not that much for kids.
You can do Six Flags on a Sat or Sun, any other day the traffic is horrendous and it can take almost 2.5 hours just to get there, bumper to bumper and slow-moving. NOT WORTH IT, unless your teenagers would only be satisfied with the park that has the most thrilling, vomit-inducing rides.
I'd definitely choose Knotts. We were there last Monday and had a fun day. Some of the rides were pretty laughable (compared to 2 weeks of Disneyland and several Disney holidays prior) but as iceskatejen says, it has better food, better employees, better atmosphere and is closer to the DLR. We did Six Flags in 2004 and liked it but decided to switch it for Knotts this year. Although both are fun to visit, Knotts is better IMO. For EXTREME rides though? Six Flags. Although Silver Bullet is pretty extreme at times. One tip if you do go to Knotts though... avoid Johnny Rockets... the service was really bad (they would just walk away mid-talking to you - what's the deal?) and the food was DRIPPING with fat. The fries were to die for though!! Have a fun trip!!
If you have young kids, knotts. Teens and up, MM. No kids, depends on what you're looking for. If you're all about the rides, MM. If you're more interested in atmosphere, Knotts.
I don't know WHAT the deal is with Johnny Rockets. The one by my house is exactly the same way. There were quite a few servers the last time I was there, and hardly any customers...and yet, it took them at least fifteen minutes before they even brought us our menus! From then on it just got worse. They had no regard for us being there, brought our food out at completely different times, finally brought my brother's milkshake after being reminded, took forever to give us the bill, and then never came back to get it. I was *really* tempted to just leave without paying because it was seriously the worst service I'd EVER had. I did end up paying, but left no tip. Another group however had a $35 bill and *did* leave without paying. Something their server just could not understand. *rolls eyes* And the sad thing is, I've heard of people having similar complaints about Johnny Rockets restaurants all over the place. I even read a magazine article someone wrote about it once. How they can stay in business with such a poor track record, I do not know.
