From what Ive experienced owning quite a few kyosho and tamiya kits, The tamiya kits hardly, if ever, broke. I run a DB01 fully upgraded beyond recognition and to be honest the only time I break is when I do something extremely stupid. Beyond that Ive smacked it into poles, walls, crashed into other cars and I never had a breakage problem. On the other hand every kyosho kit Ive had broke stuff each and every time out, would probably never buy anything kyosho again. Ive heard quite a few stories from people with zx-5's who break suspension mounts like clock work. Who needs that?
I know they perform well but confidence in your vehicle is very important.
I have so many spare Tamiya parts laying around that I dunno if Im ever even going to get around to using them. So far in the 2 years Ive owned my DB01 Ive broken maybe 2 front arms, and a shock shaft. IN 2 YEARS!. So naturally I bought me a 501x WE, skipped on the 511 for now.
I also own an AE B4 FT and a LOSI XXX-CR, yes they are 2WD I know. Both are good but Ive found the Losi more forgiving and more durable than the B4. You gotta be on your A Game with that kit at all times, otherwise itll turn around and bite you in the a$$. Its also broken way more times than my XXX-CR. So although some Losi kits are fragile I would buy a Losi over an AE any day, But above all Tamiya quality is unmatched. I also have heard good things about the D4s.
Just some input from experience.