The Nokia Lumia 620 is a great effort from Nokia with a standout design that will appeal to many, especially the younger audience. This Windows Phone 8 device features a 3.8 inch touch display, 8GB of internal storage which can be expanded through microSD, a 5 megapixel camera capable of 720p HD video capture, a secondary camera for video calls and is powered by a 1GHz dual-core processor with 512MB of RAM.
The Lumia 620 does face some competition in the form of the HTC Windows Phone 8S which has a thinner body, similar hardware but lacks a front facing camera. But keep in mind that the Nokia device has the Nokia app collection which enhances the value of your Lumia device.
Meanwhile the Samsung Galaxy S III mini and the HTC One V are Android alternatives which offer similar hardware specifications and a strong Android ecosystem backing it up.
So your final decision will depend on your personal preference and choice in ecosystem. Windows Phones have Live Tiles, built in Office, Nokia apps and integration with Windows 8 while Android has a huge selection of apps to choose from.
You can read a detailed review of the Nokia Lumia 620 on PhoneArena.