I have a celestron regal f-100ed and am really happy with it, I haven't used any of the other brands you had in mined. A lot of people might call me crazy but I had a kowa TSN-884 which according to a lot of websites is the "best" sporting scope and I returned it and later got the celestron 100 regal. Maby it's just my eyes but the price wasn't worth the difference. I was really impressed with the celestron.
The celestron regal 100 is over your 500 area but on other websites it cost less, B&H has the 80mm regal At $525 a lot less than here http://www.bhphotovideo.com/c/product/6 ... _80mm.html
I hope that helps