Portable fans can be of different types: tower and pedestal, desk, bedside, travel, “personal”…
Just do not forget that they cool people, not the air. They cool by evaporating moisture from our skin, and should be turned off when not in use.
They have to be positioned correctly, close enough to you; they are spot fans.
Portable fans quality
If positioned correctly and with enough capacity they can be quite effective; they can be used in conjunction with air conditioners.
Just be cautious with small low-cost fans; many of them are of poor quality and may not work properly or last long.
Portable fans range from very small plastic battery-powered fans, to fans with reasonable circulation capacity, like air circulators and tower and pedestal fans. When choosing, consider features like oscillation, number of speeds, tilt adjustment and noise… And take into account customer reviews.
Cheap plastic fans
Rather unexpectedly, many inexpensive plastic fans have a high number of positive reviews (far outnumbering the negative ones). See on Amazon: Personal Fans.
Desk Air circulators
Air circulators have curved vents to create swirling breezes; they provide a better air circulation than cheaper desk and personal small fans. When shopping, look for convenient features like tilt adjustment and multi-speed ability… A sturdy, weighted base can be important to prevent accidental tipping.
Vornado has very high-rated models, and their prices range from $30 to $70; but there are other high-rated brands: Honeywell, Lasko, Ozeri... Reviews on Amazon.com: Air Circulator Fans.
Very small battery-powered fans
Customer ratings for very small battery-powered fans range from the mediocre and junk to great. The vast majority of customer reviews are positive or very positive for the best models, but be cautious. They can be rather useless.
Tower and pedestal fans
Tower and pedestal fans are somewhere between ceiling fans and small personal fans in terms of pricing and capacity.
Their blades and their motors (and their airflow) fall well below those of ceiling fans, but their design – including their height and features like oscillation – can make them much more powerful than other smaller fans.
Pay attention to their quality, and expect online prices between $30-$70.
Tower fan customer reviews
Some Lasko, Holmes and Ozeri tower fans have very favorable customer reviews. Lower noise and un-obstructive design are features stressed by many reviewers.
Complaints about the capacity of these fans are common; many costumers say they do not move as much air as expected or claimed by manufacturers. See, for customer reviews: Tower Fans.
Pedestal fan customer reviews
Dyson pedestal fans, with their very expensive prices, have overall positive online reviews. Lasko, Holmes, Ozeri… have also positive reviews, though not as high as those of their tower fan models.
Most customer complaints are similar to those of tower models: the fans fall below the expectations in terms of capacity, and some reviewers consider them "cheaply-built" and noisy… Reviews on Amazon: Pedestal Fans.