There's an inherent bias in reviews. People who feel strongly about a product are much more likely to complain - and a bad experience is much more likely to elicit a strong emotion.
Stick with Hamilton Beach, Crock or other name brands and you'll be fine.
As to what one you should buy... depends on what features you care about. I really like the locking lid on mine since I make food and bring it places a couple of times a year, so that's a nice feature for me. I like to make really big meals to last me a while, so the 6qt model is the one I went for, but if you make smaller meals then a smaller model will be easier to clean/etc. I like the timer functions too.
This is similar the one I use: https://www.amazon.com/Hamilton-Beach-Programmable-Temperature-33969A/dp/B00EZI26GO?th=1
I have the Hamilton Beach Set it and Forget it 6 quart slow cooker. I love it. I'd reccomend getting the 6 quart size even if you aren't cooking for a lot of people. It's very annoying to want to cook something in there and not have enough room, so 6 quarts has been pretty good for just about everything I want to put in there. I even once (barely) fit a whole chicken in that thing! Here's the amazon link: http://www.amazon.com/Hamilton-Beach-33969A-Programmable-6-Quart/dp/B00EZI26GO/ref=sr_1_3?ie=UTF8&qid=1404759563&sr=8-3&keywords=slow+cooker
We’ve had one of these Hamilton Beach for probably 6 years and recently bought a second one for the RV. I think they are a fair value and pretty good product all around. https://www.amazon.com/gp/product/B00EZI26GO/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
I absolutely love this one by Hamilton Beach. I've used plenty of slow cookers over the past few decades and this is simply the best. It's large enough for every recipe I've ever made, programmable (by time/temperature), reliable, easy to transport and easy to clean.
I've been using this one for a few months now.
Only costs $50 and I got a 9 lb pork shoulder stuffed in there that fed me for a week.
I’ve bought two of these Hamilton Beach ones and I’m satisfied with them. The first I’ve had maybe 5 years and more recently bought the same one for the RV.
I have the exact same model and absolutely love it. Not a negative I can think of.
Edit: I actually have this one: Hamilton Beach 33969A Set 'n Forget Programmable Slow Cooker, 6-Quart https://www.amazon.com/dp/B00EZI26GO/ref=cm_sw_r_udp_awd_AoNMtb01QPR2BN8W
More bells and whistles, programmable, temp probe, etc
I just got a new slow cooker and it has a rubber seal around the edge of lid. It's like this: http://www.amazon.com/Hamilton-Beach-33969A-Programmable-6-Quart/dp/B00EZI26GO/ref=lp_289940_1_3?s=kitchen&ie=UTF8&qid=1402776439&sr=1-3
I've had this one for a while (4 years?) And love it! I think it meets all your requirements. https://www.amazon.com/dp/B00EZI26GO/ref=cm_sw_r_cp_apa_9PJoBbMKYHPNB
Wow. That seems a lot to spend on a slow cooker. I can't think of any that are unsafe.
The Ninja seems pretty cool. http://www.amazon.com/gp/aw/d/B0093MRWJS?pc_redir=1412516198&robot_redir=1
Personally I'd like a slow cooker that has a latch down top for transport and has some programing features. Something like this. Hamilton Beach 33969A Set 'n Forget Programmable Slow Cooker, 6-Quart https://www.amazon.com/dp/B00EZI26GO/ref=cm_sw_r_awd_JFKoub0NQ90J3
I have a Hamilton Beach similar to lborloz's. I love the different settings and the temp probe. I highly recommend spending a few extra bucks!
I have this. I cook for one and occasionally give a bowl of stuff to a friend. I never have problems with scorching because I always make enough for at least two. Like, I'm going to use 1.5 - 2 chicken breasts because I want leftovers so I don't have to cook for a couple of days.
Plus, the bigger slowcooker is nifty because when I make soup, the thing fills up.