iMac 21" for web (PHP) development?

It's not what I would reccomend.

The CPU is from a macbook air, it's fine but not what you want in a desktop.

I wouldn't buy any computer without some sort of SSD involved in this day and age the speed advantages are just to nice to miss out on.

If you are using multiple VM's then RAM is a priority and the 21.5 inch iMac is non-upgradeable.

I'm not syaing that an iMac is not what you want just not that one mid tier with a desktop CPU and 16Gb of RAM (unusual for me I usually say stick with 8GB but I think you may need more in a few years time) and at least a 1TB fusion drive (although with only 24Gb of SSD the 2TB is a much better option with 128GB SSD).

Of course this may be way beyond your budget in which case a new windows desktop is probably a better bet.

 

I'd get something with a little more power. Especially if you're thinking about running vm's. 16 GB of RAM would be good and an SSD, or a fusion drive. That will go a long way to make things run smooth for a long time.

 

Look at the refurbished section of your local apple store website. Models come and go so just keep an eye on what the prices are and don't rush. Sometimes you will find a 27" model for a similar price than the 21" retail and you would be able to upgrade the memory yourself when needed.

For a computer you wish to keep 3+ years, I would avoid buying the new base 21" model. It's really just for light use. Between low fixed memory, slow HDD it would be frustrating to use.

I have a 2010 model: (16gb ram self installed), i5 3.6GHz, 256GB SSD (self installed) and it's coming on 6 years old and honestly would do what you need and not miss a beat. You should look into buying a used iMac 2010-2012 off a local for sale site. Since it's your first step into OS X usage maybe it's a good idea to buy a well maintained home model from someone for 50% or less.

 

Is there any reason why you had to use a VM to do PHP development? Apache, PostgreSQL and Netbeans are all available natively for Windows but you aren't using them. I am not tryint to discourage you from purchasing a Mac but you stated that running those programs natively was one of the reasons you wanted to upgrade.

As far as the iMac is concerned, do not buy the cheapest model. I would say that you get what you pay for but performance wise, you don't even get that.