I've been partial to the Cointerra ever since I saw it.
Looking at the charts, it does seem to be the best bet. But, I'm a little apprehensive because of the tsunami of ASIC's hitting homes in the next 1-3 months.
jungle_dave summed it up very well (I hope your KnC(s) start shipping soon) and Andrew, you hit the nail on the head; all we can do is look at charts at this point. We also have to remember that out past 3 months into the future, any projections we can do start looking crystal ball-ish. Us miners *hope* the crazy growth will level out soon but it may not be until Spring. It could turn out that this crazy new growth is the norm and it *could get even worse* and in a few years we could all end up laughing about the relatively slow network growth of the fall/winter of 2013, when compared to future norms.
However, if you're willing to trust this crystal ball & look at those charts on TGB, 90%+ of the returns are made by that 6-7 month mark:
http://mining.thegenesisblock.com/a/9bf8dae935This assumes a January 1, 2014 start date which is being optimistic. You'll note that the profit for this miner is made by the 5th month using these projections w/ ultra cheap electricity, another advantage of doing a Group Buy with me, and actually shows that the miner should probably be sold at the *five month* window instead of 6-7 because returns diminish considerably but the unit may still have higher resale value (being in-hand; there *still* could be a shortage of in-hand hardware if the mining market continues to expand in size and diversity).
Where we could run into issues is the same thing that bedevils any GB: slow delivery from mfgs. The delivery could be on January 30/31 for this CTII & it would still end up being a January delivery with none of the benefits of running for the whole month of January. That's how small the margin of error has gotten.
Even with amazingly low 4 cent kWh electricity, a Bitmine 500GH/s in December *still* shows a loss:
http://mining.thegenesisblock.com/a/9675b58987=============================================================================================
Most people have done their homework on these GBs & come to their own conclusion whether to pass or proceed. Taking off my salesman hat for a minute, which is not the usual role for a GB Coordinator at this point: It appears to me if you're using these projections as a guide, one shouldn't even mine! You should just buy & hold like many people have voted with their wallets this month:
https://bitcointalksearch.org/topic/poll-sept-2013-asic-miner-survey-291775However, these Group Buys are for those that think that pure buy & hold is plain boring even if it's estimated to give the best returns compared to mining at the moment. One thing to keep in mind about the mining calculators we all use: they're all just algorithms, and while algorithms help rule and control the world around us, they're only as good as the data, rules, and models that you build into them. These algorithms can only estimate for factors such as future network growth & plain ole luck favored with math: like BTCGuild getting 6 discoveries in a row in the same day (150BTC on those ones alone).
Group Buys are good for getting the very best values (at cost in my Group Buy's case) and hedging your bets by spreading your bets among what you think are several strong contenders as far as mfgs. *and* GB Coordinators.
For myself, I Buy & Hold & do dollar cost averaging twice a month on BTC coin purchases but I also have pre-orders in with BFL (2 Jallys; ebay sold & funds applied to HF), 1/4th of a HashFast Baby Jet (Round 1 Group Buy), a couple of 2-2.7GH/s USB thumbs from Barntech, and a couple of shares (so far) in what will likely be a Cointerra or Bitmine unit...because I'm one of those that think pure Buy & Hold is boring while still practicing the general benefits. I also own shares in AM as mentioned and 13 shares in the mcxNOW exchange that pays interest on deposited BTC and fee payouts for all activities on the exchange.
I also love arbitrage and serving as a trusted middleman as a means to make money or BTC *from* the Bitcoin phenomena. I also have a Feb. 22 $30K rig pre-order worth 1.5TH/s for sale as an ebay conduit for a forum member in Canada:
http://www.ebay.com/itm/ASIC-Bitforce-Mini-Rig-Bitcoin-Miner-Butterfly-Labs-3x500GH-s-Feb-22-2013-/130993541777?pt=LH_DefaultDomain_0&hash=item1e7fd2d291I may have to drop the price for it but I'm starting it off at that price. I'm obviously not your lawyer or your financial adviser, but I'm using this ebay auction, and my BTC related investments, as examples that there's tons of ways to skin a cat in this new BTC economy besides buy & hold or solo-mining.