I know that you can buy lots of things online and that prices are competitive online, however, you do need to know exactly what you are buying, and, given that you have posted this question here, you might not be there yet...
Please visit your local bike shop, explain to the sales staff what you are looking for, what distance you are having to put in, whether that is going to be all on roads or on trails, whether you are going to be a fair weather cyclist and what you are going to need to carry. Also mention what sort of money you were looking to spend.
Then let the shop show you 2-3 bikes that meet your criteria. See how the bike feels and, if they will let you, go on a short test ride. Ask about the brands pulled out the rack and why the shop sells them. Also, ask about how much the accessories will cost. You might need lights, you might need the tyres changed for the road and you might want a lock. Hi-viz clothing, a track pump and maybe a helmet also comes into the deal, you will be able to better negotiate a price if you include the accessories - a lot of bikes have a price that the shop (online or otherwise) has to sell at or else they lose the dealership rights, they cannot do a deal on that but they might be able to do a deal on the accessories.
Customisations can work out better of buying from the shop as swapped out tyres can be put back into stock. The same with a seat and pedals (if you go clipless).
Remember that your local bike shop have to compete with the online box shifters, they may not be able to do so on absolute price but they certainly can with service. They are easier to get to for a warranty return and they may well put a free service into the price.
Shops also have cosmetically 'shop soiled' bikes that work absolutely fine but have incurred a scratch during their time in the showroom. You can negotiate a price on these, particularly if they are a 'last year's model'.
Size is really important. Given that you are 6 foot+ you will be needing to look at the 'Large' size or maybe the 'X-Large' size. You can only determine which is best for you for a given brand if you go to the shop. Remember they might not have your size in your preferred model on the showroom floor, they may have one in the warehouse or be able to get one in for you in a matter of days. So, just because your preferred model is not there in your size, don't be put off - try the next model up if it is in your size and then try to order the model/size you do want.
As for your weight, that should not be a problem. However, you will need to keep those tyres inflated to the value shown on the sidewalls if the wheels are to survive. The best way to keep tyre pressures good is with a track pump, these come with a gauge and only take a minute or two one a fortnight/month.
After visiting the local bike shop and finding something you want, you can go online and get a better price. This mail order bike will come in a box and you will need tools and a spare weekend to get it right. If you order from the shop then they will do all that for you, usually to a higher standard than you can do yourself. Plus you will be saving postage. If the local bike shop accessories (e.g. lights) are bought with the bike then expect them to be fitted too.
Hope that helps!
