Updated from 11:15 a.m. EST

Aggressive Black Friday promotional events had shoppers stampeding into stores throughout the post-Thanksgiving weekend in search of savings, but a wide disparity between two shopping reports left investors trying to make sense of the results.

The National Retail Federation estimated Monday that retailers recorded sales of $27.8 billion over the weekend. Total sales, including online sales, rose 22% from last year, with discounters and electronics stores attracting the most customers. On the basis of its surveys, the NRF said the average shopper spent $302.81.

Separately, ShopperTrak said consumers spent around $8.01 billion last Friday, down 0.9% from last year. It said Saturday sales were flat compared with those of last year at $5.4 billion.

"We saw some very deep discounts being applied through the retail space," said Bill Martin, ShopperTrak's co-founder. "When that happens, it's very difficult to live up to last year's results."

Traders were recently erring on the side of caution, with the S&P Retail Index down 1.5%. The index is up more than 6% in November.

Both NRF and ShopperTrak cited a decidedly promotional atmosphere in stores over the weekend, and the differences in their methodology shows who benefited from the bargain-hunting.

The NRF gathered its data by surveying 4,209 consumers about their shopping progress, and the results included those people shopping online and away from malls at big-box discount chains like Wal-Mart ( WMT), Best Buy ( BBY) and Home Depot ( HD).

Meanwhile, ShopperTrak monitors store traffic only in malls, so their results left out online shoppers and many of the off-mall outlets that are growing in popularity, particularly when it comes to promotional events the day after Thanksgiving.

"Value is the key for a lot of consumers this year, and that's particularly true for those shoppers going out in search of big deals on Black Friday," said Scott Krugman, a spokesman for the NRF. "Shoppers out on Black Friday are looking for door-busting deals, so they gravitated towards big discount chains rather than specialty stores and mall-based stores that can't compete in price. But these stores will probably do better as the season goes on and other people come out to shop."

Both groups identified sales of electronics, such as flat-screen televisions and MP3 players, as a dominant category. This bodes well for the likes of Best Buy, Circuit City ( CC) and Apple ( AAPL).

"We're obviously headed into a very promotional holiday season -- the most promotional we've seen in years," said Dan Hess, chief executive with Merchant Forecast LLC. "The safest place to be is with those stores that know how to promote and make that part of their year-round strategy."

Aside from discounters like Wal-Mart, Target and Sears Holdings ( SHLD), Hess cited department stores as potential winners, like Federated's ( FD) Macy's chain, and a few specialty chains, like New York & Co. ( NWY) and Children's Place ( PLCE).

On the other hand, many mall-based chains that have trouble competing with larger rivals in price-cutting could have a tough season. Specialty chains like Gap ( GPS), Limited Brands ( LTD) and Ann Taylor ( ANN) may suffer.

Last week, the NRF raised its sales forecast for November and December to a 6% increase from its previous estimate of a 5% gain, citing declining gasoline prices. That marks a decline from last year's 6.7% increase, but it would be the second-biggest gain since an 8.3% jump in 1999.

The world's largest retailer, Wal-Mart, drove heavy traffic by offering deals such as laptop computers for $398. The company reported that its November same-store sales were headed for a 4.3% gain. Those results would land at the midpoint of its previous guidance for an increase of 3% to 5%.

Strong growth expected in online retailing this year may well extend the Black Friday shopping surge into this week for what some observers are calling Cyber Monday. Consumers are expected to take part in online sales promotions as they return to their computers at work.

On Sunday, Visa USA said retail spending on Visa credit and debit cards rose 11% to $3.7 billion over the weekend. Barry Ritholtz, chief market strategist with Maxim Group and a contributor to RealMoney.com, said in a research note that this may not be a good sign.

"This implies that consumers are stretching to spend money they do not have," Ritholtz said.

Hess said things look good for the industry as a whole so far, but he said there is a risk that promotions will get out of hand.

"If a lot of retailers start to panic and start escalating aggressive promotions sooner than they planned for, then profit margins could be at risk," Hess said. "Most of what we saw this weekend was well-planned in advance and built in to margin plans."

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