Should I buy a premium underlayment, or save money and by buy cheap?

Underlayments are generally sold in rolls of 100s/f. Prices range from $25 to $80 per roll, translating to an extra $0.25 to $0.80 to your flooring cost. Often, homeowners reduce the overall total cost of their flooring purchase by purchasing a cheap underlayment. This is not a good idea.
Underlayments are an important aspect of laminate floors for two primary reasons. Firstly the quality of your underlayment has a direct effect on how the floor feels and sounds underfoot. Secondly, the underlayment will affect the wear and tear of your floor.
Underlayments server the following purposes:
Moisture protection
Thermal insulation
Impact sound absorption
Hinders mould growth with anti-microbial additive
Help prevent dust mite colonies
Smooth minor subfloor imperfections

Impact sound absorption:
The main factors that affect the sound are the thickness and density of the underlayment. Underlayments range from 0.075in to 0.25in in thickness. Because laminate flooring is a floating floor, i.e. it is not fixed to the sub-floor, the floor tends to give off the sound when walked upon. Thicker underlayments offer more sound reduction.
Additionally, denser underlayments also reduce sound as well as offering more stability. However, thick underlayments with low density can add instability to the floor as they are compressed when walked upon, and this will be felt underfoot. In particular, natural cork underlayments are very good sound insulators, as well as being very dense. If you live in an apartment and people are living below you, sound absorption is a very important factor. If you do not install a sufficient sound barrier, your neighbours will hear you walking on the floor, and this could result in you having to remove your new floor.
Thermal Insulation:
If you live in a cold climate, thermal insulation is an important factor. Thicker underlayments act as better heat insulators and barriers. Radiant heat panel underlayments are also available.
Moisture protection:
Moisture rising from a damp subfloor will slowly destroy the core of your laminate flooring. To combat this, your underlayment should have some form of vapour barrier to protect the underneath of the floor from subfloor moisture. Some underlayments are an all-in-one sound and moisture solutions, while others are either sound or moisture barriers. Regardless of what type of sub-floor you have, installing a moisture barrier is essential.
Hinder Mold Growth with Anti-Microbial Additive and prevent dust mite colonies:
If you live in a climate where mould growth is common, you can install an underlayment with an anti-microbial additive. If your sub-floor is wood, this type of underlayment can also prevent dust mite colonies.
Smooth minor subfloor imperfections:
Generally speaking, laminate floors can only be installed over level sub-floors. If your floor has minor undulations, a thick, dense underlayment can help to smooth out the undulations. Note that this is only for minor undulations. Floors with serious undulations must be levelled before installing a laminate floor.

Kids and Pets! How Long Will my Wood Laminate Flooring Last?

I have an active household with young children and pets. Will wood laminate flooring handle the heavy wear and tear?
Yes, provided you install a good quality wood laminate floor.
Today, reputable laminate manufacturers must submit their flooring to the European Producers of Laminate Flooring (EPLF) for rigorous testing. The EPLF is an independent organization which aims to set standards for the laminate flooring industry. Floors submitted to the EPLF go through a series of tests that evaluates a laminates resistance to stress and is then given a rating code according to its performance. They test the floor for resistance to scratches, burns, fading, stains and impact. If the floor fails any of these categories, then it is not certified.

Pergo – Coastal Pine Wood Laminate flooring

Pergo – Highland Hickory Wood Laminate Flooring

The following is the AC rating guide and this will assist you in determining if a floor is suitable for your specific needs.
AC 1: 21 (Residential, Moderate traffic: Suitable for bedrooms or guest rooms)
AC 2: 22 (Residential, General traffic: Suitable for living rooms and dining rooms)
AC 3: 23 (Residential, Heavy Traffic: Suitable for all areas)
AC 3: 31 (Commercial, Moderate traffic: Suitable for hotel rooms, small offices)
AC 4: 32 (Commercial, General traffic: Office, restaurant, boutique, café)
AC 5: 33 (Commercial, Heavy traffic: Public buildings, department stores)

Although AC1 is rated for moderate traffic and suited to bedrooms, if you have young active kids you are better off going with an AC2 rating for their bedrooms and play room. Small pets will not have much impact on your floor. However larger dogs can scratch the laminate surface. If you have large dogs at home, it is advisable to get a better quality laminate that meets a minimum of an AC2 rating. However, AC3 would be optimum.
North American Laminate Flooring Association (NALFA)is the US equivalent of the EPLF. NALFA is the organization that sets the standards for laminate flooring in the USA. NALFA is a non-profit organization, and its members are unpaid volunteers. Laminates submitted to NALFA undergo a range of stringent tests. If the laminate floor meets or exceeds NALFA standards, it will earn the right to display the NALFA seal of approval. Note that submission of laminate flooring to NALFA is voluntary. The following laminates carry the NALFA seal of approval: Clarion Laminates, Columbia Flooring, Kronotex USA, Mohawk, Quick-Step, SHaw, TORLYS, Pergo, Mannington Mills. A complete list of NALFA approved laminate flooring brands can be found at the NALFA website.
The combination of kids and pets results in constant heavy traffic in the main living areas, and it is advisable to purchase a wood laminate flooring with an AC3 rating. Although these floors are more expensive, they will stand the test of time and still look good after many years of heavy use.
If you have an active household, stay away from floors that do not have an EPLF certification as chances are these floors are not good quality and would not pass the EPLF test.