There are literally dozens of service plans to pick from now on all four nationwide carriers. Making sense of all the options can be dizzying.

Do you buy or lease? Do you care more about network quality or price? Do you want a contract, or would you prefer to pay in installments?

To sign up for the right plan for the iPhone 6S or 6S Plus (on sale Friday), you have to understand your own cell phone habits, and figure out what's most important to you first.

To help you decide which plan suits your budget and phone usage best, CNNMoney studied device deals and service packages from Verizon, AT&T, T-Mobile, and Sprint. We also examined Apple's new iPhone Upgrade Program and payment plans.

There is no one perfect plan, but each has its benefits.

Here are some questions you should ask yourself before choosing the one that's right for you:

Do you want to have a new iPhone the moment it comes out?

Then sign up for a lease or iPhone upgrade program from T-Mobile, Sprint, or Apple.

Sprint: Of all the lease and upgrade plans, Sprint's "iPhone Forever" plan is the cheapest. Right now, you can lock in a promotional -a-month deal for 22 months for an iPhone 6S with the trade-in of an old smartphone. Without a trade-in (or whenever the promotion ends), you'll pay $22 a month for 21 months. A 6S Plus will cost four dollars more per month.

T-Mobile: T-Mobile just slashed monthly lease prices on the iPhone 6S and 6S Plus to $5 and $9 per month with an iPhone 6 trade-in. The limited time deal is part of T-Mobile's "Jump On Demand" plan, which gives you the option to upgrade to a new phone up to three times a year, and T-Mobile kicks in insurance for lost and stolen phones too.

Joining Jump On Demand is an 18-month commitment. After 18 months, you can choose to pay $164 to keep the phone, give it back and start another lease in exchange for a new phone, switch to a monthly installment plan to buy another device, or leave T-Mobile.

Apple: Under Apple's iPhone Upgrade Program, you'll pay $32.41 per month for a new unlocked device. The price also includes two years of AppleCare+, which covers hardware repair, software support, and two accidental damages.

Unlike T-Mobile and Sprint, however, Apple (, Tech30) will only let you upgrade after 12 payments. (And Apple doesn't provide phone service.)

Some things to consider with these plans: First, you don't get to keep your old phone once you upgrade. Apple iPhones retain their value better than any other smartphone, so you could miss out on a chance to sell your old phone on a booming secondary market.

Second, if you don't want to give your phone back, you do have an option of buying it at the end of your lease. But you may end up paying more than the retail price. T-Mobile is the exception: You actually end up paying $125 less than retail price if you choose to buy your phone after your lease is over.

Third, each phone upgrade restarts the clock on your lease, so you pay for phones in perpetuity without ever owning your device.

Source: money.cnn.com