Re: I wanna purchase lumia 1520 but my friends stopped me due to lumia applications
Your friends statement is actually two fold.
First is the assertion of is the Windows phone ecosystem a good OS to invest in? That is were the app comparison really matters. I'd agree with your friend on certain apps. Of course the trending apps like Instagram, Twitter, and others have gotten rare updates while their iOS and Android counterparts are been updated rather recently. Now if you're all about first party apps, then you may want to consider another OS, however I'll implore you to try some of the third party renditions, and you just might find they work as good if not better then parent apps they emulate. Take 6Tag, or a couple of Twitter client apps for example. How familiar are you with the Windows phone OS will go a long way to determining how you'll like the 1520.
Second is how does the 1520 stack up against other Windows phones? Again this is based on how you're going to be using it. I've had my 1520 for year now, and to be honest no other windows phone really rivals it in terms of display, processor, memory, battery life, storage capacity, or camera combined. The biggest deterrent may be that MSFT has recently discontinued selling the 1520 which implicates there may be a replacement coming at some point. I've actually been intrigued by the 640XL which although has reduced specs, they are still respectable, and it's the newest phone out with preconceived Windows 10 for phones planning into the build.
Ultimately if you can get one at a good price, you won't be disappointed. I am going to wait for a more equivalent replacement for the 1520 because to be honest, there's really nothing out there right now that can stack up to it.