The best mall overall is the Florida Mall, with a good cross-section of stores and will not necessarily be over expensive.
The Mall At Millenia is probably the nicest (and newest) but possibly not the best for bargains with some very exclusive stores - often you wonder if anyone actually goes in some of them as there always seem to be 2 or 3 smartly dressed staff waiting to pounce.
Both of the above have very good Department Stores such as Macy's, Bloomingdales at M&M, Dillards,Burdines, Lord & Taylor, Nordstrom and Saks 5th Avenue at FM where you can get good value for money.
There are also JC Penney and Sears which tend to be not quite as upmarket as the other depeartment stores at the Mall.
Both M&M and FM also boast excellent food courts.
For ladies fashions you are probably better off in one of the better Department stores where they do DKNY/Ralph Lauren etc ..there are plenty of women's stores within the malls, I know as I am often waiting for my wife outside them!! there is one called Anne Taylor which she likes and a couple of unisex stores to watch out for American Eagle and Abercrombie & Fitch.
Festival Bay is a fairly new development too and gets better each time we go, and is very different from the standard mall with very unique shops including the Ron Jon Surf Store. However, a lot of the plots remain untaken and it is taking time to fully develop, it has the potential though.
There are a couple of malls a bit further away such as West Oaks and Fashion Square, but FM and M&M are the best.
All the malls but particularlt FM and FB, also have some excellent stalls that sell quality perfumes and jewellery in particular.
As far as bargains go in Orlando, Premium Outlets is the best one, although as with all discount shops can be a bit hit and miss as most of the goods never sold at the bigger stores originally.
Similar are the Lake Buena Vista Factory Stores, possibly not as good as PO, a lot of the stores are US labels you will probably be unfamiliar with.
Generally there are bargains to be had pretty much anywhere, especially on sportswear - there are a number of Nike outlets in Orlando - naturally the best bet are US labels like Nike, Oakley, Levi's etc
Jewellery and perfumes are generally also cheaper in the malls than they are here in the UK.