What is the best bitcoin miners
The only LEGITIMATE "best miner" offered to the public at this time is the S7 for Bitcoin and other SHA256 coins.
This should change by sometime in December when Lktec (probably using Innosilicon A3 chips) offers their announced 5TH unit.
It it probably that a few other companies have equally efficient equipment in production, but Bitmain and Bitfury don't sell to the public any more, Spondoolies is apparently also no longer planning to sell units to the public, and Avalon has made no announcement about anything competative (though they could have something in the works but not announced).
KnC was good on performance, WHEN they worked, but the reliability of the company and of their miners was generally very poor to outright crap.
There have only ever been 2 chips that could "switch" from SHA256 to Scrypt (technically, they were both designed to mine BOTH at the same time) - the Gridseed GC3355, and the SFards SF3301. Sfards was formed from a merger of Gridseed and Wiibox, so the SF3301 is in reality a second generation of the GC3355.
NEITHER of those chips were particularly efficient at SHA, both were fair efficient at Scrypt when introduced but the introduction price was VERY high in both cases - and as the SF100 miner based on the SF3301 is pretty close to brand new the price is STILL way too high to be viable.
Gridseed/SFards has a good track record on chip design but a VERY POOR record on board-level design - and based on the very few reports I've seen of SF100 units in the field, they have some serious issues with "not working reliably".
The other factor to keep in mind is that you'll find more shares and get more rewards from mining Scrypt coins, but ALL of them are worth a lot less than Bitcoin - commonly around 1% OR LESS of a Bitcoin (LTC is a hair over 1% right now but dropping pretty fast since it's pre-halfing runup).
Innosilicon has announced tapeout of both an A3 (SHA256) and an A4 (Scrypt) chip design, but no hard specs on either yet.
Possibly in production before the end of the year, but NOT YET AVAILABLE.
Welcome to the shakeout year of 2015, when the bubble collapse killed some of the legit companies and most of the attempted scammers.....