"Manufacturing" may require features of an accounting package that aren't available from all providers - if you want particular features, such as stock control, order processing, bill of materials, etc., then you have to look very carefully at your accounts package - not just as to whether or not they offer the features, but how user-friendly they are. Can't recall the exact details, but I once had a client using Quickbooks which was absolutely fine for the accounts/book-keeping side of things, but was a real pain in the neck for the sales-force as they couldn't search on products in the way they wanted - at that time (old version, hopefully corrected now), you could only search on certain parameters, i.e. search by product number but not by product description, or something like that. It really affected the sales personnel, slowed things down and sometimes resulted in lost sales if they couldn't find the product a customer wanted.
Same with "selling online". Ideally, you want something that integrates with your website database so that stock control can be kept up to date across both systems and also so that sales via the website can be automatically transferred through to the accounts side of things. Many e-commerce platforms have built-in links to accounting software to facilitate this, so a good place to start would be asking your e-commerce provider for a list of supported accounting packages. There's little point in getting the best e-commerce package and the best accounting package if they won't "talk" to eachother!
I'd suggest you look at some of the online accounting packages as they seem to be more switched on to e-commerce and online trading. Google for "Kashflow" and "xero" which seem to be the two most popular at the moment.
Sage & Quickbooks may be the most popular, but that's because of historic market dominance. I don't think either are regarded as "the best" these days and both seem to be high cost and high maintenance when you factor in the ongoing support contracts and the need for program updates every few years.