First of all, I do NOT try or install and definitely would NOT pay for any app that receives less than 4.0 rating on Google Play.
Best apps I've paid for:
CamScanner: The best document scanner app for doing my job.
Handy Scanner is also very competent, but I only need one app for scanning purpose.
DW Contacts & Phone Dialer: The most customizable contacts and dialer, although its customization menus and options are unnecessarily complicated and have many redundancies.
Delayed Lock: The default phone lock activated too soon and too often; it was driving me mad until I uninstalled this app to override the default phone lock settings.
Dr.Web Anti-Virus: The most non-intrusive anti-virus app with the smallest footprint among anti-virus apps. Just do NOT use or turn on its broken and unnecessary anti-theft feature.
Fast Reboot Pro: It automatically clears RAM and caches every time I unlock my phone, keeps my phone snappy.
Folder Organizer: The single most useful app I have on my phone, keeps my apps and home screens organized.
Mobi Calculator Pro: The calculator with the best history function, allows me to edit and add notations to history entries, which really helps me do my job.
Quick Boot Plus: The reboot app I like the most, simple and clean.
Relax Melodies Premium: I have trouble sleeping, this has really helped me fall asleep fast. I am using it every night.
SetCPU: A nice battery saver. Previously I also used it to prevent my phone from overheating. However, I replaced replacing the manufacturer batteries with a third-party one, which resolved the overheating problem.
SystemPanel App/Task Manager: The interface is very beautiful, user-friendly and informative. I use favorite it in another app/task manager,
Smart Task Switcher Pro, that pops up whenever I tap on the Home key. (Smart Task Switcher is not too great on its own; it has too many problems, and the developer has not fixed or updated it since last year.)
Titanium Backup Pro: I use it to uninstall bloatware, moving apps in and out of /system. This is my primary backup app because ClockworkMod does not work with
Link2SD installed.
Best games I've paid for:
Battleheart, (the
best action RPG for Android phones; it is a pity the developer announced in March that they had given up the Android market and ceased all productions for Android. I shall miss Mika Mobile,)
Battle for Wesnoth, (the PC and iOS versions are far superior and receive new updates way more frequently, but this is still the best strategy game on Android,)
Dungeon Village and
Game Dev Story, (I started playing KairoSoft games and loved both. I want to get all of them,)
Majesty: Fantasy Kingdom and
Majesty: Northern Expansion, and
Rebuild.
Wastes of money (for me anyway):
Juice Defender Ultimate: It worked, but it also
severely slowed down my phone. The developer also has not updated the app since last year.
OfficeSuite Pro+: This is absolutely the
WORST office app... let me scratch that, this is the
WORST app that rips off people.
PERIOD. Before you pay $15 for the "Pro" version, it does not reveal that people will have to pay $5 to $10 for each additional component (e.g.,
Windows-compatible fonts, spell-checker, dictionaries, etc.) You do not have to buy the extras, but the app keeps bothering you with sale pitches. Thank goodness I got it free from Amazon AppStore and did not get ripped off by it.
ROM Manager Premium: ClockworkMod does not recognize or format /sdcard/_ExternalSD correctly on my phone. It also does not work with
Link2SD and therefore cannot backup anything correctly. For me personally, Link2SD is the one single must-have and my number-one favorite app. Link2SD conflicts with ClockworkMod, so it makes ROM Manager unusable on my phone. I can have only one of either Link2SD or ClockworkMod, and I choose Link2SD, so ROM Manager would have to go.
ROM Toolbox Pro: Has a classy stylish interface. It does a lot of things and duplicates most of the functions of Titanium Backup and ROM Manager, but it does not do anything particularly well.
Widget Lockscreen: I used it for a day before found out
Go Locker is free, better and has more options.
Beautiful Widgets, which I am still using, may also become a waste because the
GO Launcher EX version (which is free) is updating and improving fast. All the free GO Launcher EX components and giveaways are quickly outclassing all their competitions and paid counterparts.