I will give my opinion on the 5 boxes on your list that I have listened to.
M90- well known to all collectors as the "King" of boomboxes due to its superior sound, built quality, and performance on batteries. A large boombox with 8" woofers and 2 1/2 tweeters. Perfect for any outdoor setting with its ample power. It has clean tight bass, crystal clear highs and wonderful sound separation...and it's plenty loud. There is a reason it is at the top of most collectors list and why the price for them can go up to $2000.
M70-the M90's little brother and the benchmark for all medium sized boomboxes. Another collector favorite and with good reason. It has monster power for its size, top notch build quality and a fantastic tape deck that is bullet proof. it has hard punchy bass, crisp highs and lasts forever on batteries. It also has an available carry strap that makes it the perfect carry around boombox. It also happens to be my favorite boombox. Can be found for as little as $200-$300 up to $650.
Panasonic 5350-a powerful supreme quality boombox that most would never take outdoors. Its sound quality rivals the M90...its that good. The M90 has better highs but the 5350 has better bass. These are rare and very expensive. Expect to pay up to $1000 for a good one.
Conion C100f-a raw beast of a street machine. Crazy loud, strong bass and killer looks. Its louder than the M90 but lacks in built quality. It has decent sound but is a little raw compared to the M90. Very popular among collectors and expect to pay up to $1500 for one in excellent shape.
Aiwa 660-about the same size as an M70. It has very warm sound, smooth deep bass, crisp highs and a wonderful tuner. This one is a must have sleeper if you love good sound. These can be found for about $75-$100 if you are patient when looking. Sounds comparable to an M70 with deeper bass but the M70 crushes it on power.
Just kidding these all vary depending on their condition (complete, working, cosmetics) and most importantly, what their worth to You. Sometimes certain models that usually fetch $600-800, will fetch $350 if no one else is bidding on them at that particular time.
