I’m looking to purchase an IMac.

What kind of speed do you need? A: Booting the system, saving and optening files and launching applications or B: speed in an app like image or video editing or processing?

The first, A, is achieved with solid state drives. Get as large a drive as your budget can afford and then you can add additional rotational HDs for file storage thru external HDs from macsales.com.

The second, B, is achieved by increased RAM. If you get a 21" iMac then purchase as much RAM as offered because it is not user upgradable after purchase. If you get a 27" iMac get the basic 8 GB and run with that to see if it meets your needs. If you find you need more you can get additional RAM modules from Crucial.com or macsales.com at less than 1/2 the price that Apple charges and you can install them yourself.

As for which CPU to get that will depend on the type of processing you intend to do. If you do a lot of heavy duty image and video editing you will want to go with one if the faster i5 chips or the i7 chip.

So do what rkauffmann87 suggested and visit an Apple store, tell them what type of computing you'll be doing and test drive the type of iMac that they suggest.

No virus protection is needed as Mac OS was designed from it's very beginnings almost 20 years ago to be extremely secure. Most users enjoy years of trouble free operation if they simply keep Mac OS up-to-date. It is unwise to install any antivirus, cleaning or any other third party "maintenance" utilities as they simply are not necessary and tend to create far more problems than they ever solve.

As far as which iMac is right for you I strongly suggest visiting your local Apple Store or Apple reseller so you can describe what your needs are and they can help you match that to the right computer.

As there are two different size iMacs (21.5" & 27" displays) that would be the first decision you need to make. At the very least get one with 16GB of RAM and a Fusion drive. If you want the fastest available then consider instead of a Fusion drive buying one with a SSD, the advantage being speed and reliability as there are no moving parts with a SSD. However again, for exactly which configuration is best for you, please visit your local Apple Store.