Whats a good Digital painting app?

   I really want to get better at digital painting, proportions, picture layout and faces, but mainly just the digital painting bit, and by that i mean i want the paintings i do to actually look like whatever i'm drawing. I've seen a lot of the work other students have been working on and frankly I am amazed, it's really sparked my interest again and i want to start up again.
   After trying with my Wacom bamboo I've got a bit better from when i started, but i don't have the time i'd like to sit at my computer and do any digital painting at all really. I'm away from my computer a lot of the time, either on the train (4 hours per week), at home (3 days per week) or just generally out and about (Not really sure, but you get the picture), and the time i am at my PC i'm either posting on here, doing some 3D modeling or, i'm afraid to say, just procrastinating.
   So I've come to the conclusion of getting myself a tablet, i could go through all the tablets that I've been looking at but its not really that important. After a bit of thought (not a lot really) I've decided to go for an Ipad, mainly because for some STUPID reason, some of the good applications are only available on iOS, so to avoid the inevitability of me finding an amazing app that i really want and then realizing i cant friggin' have it, I've just thought sod it! I'll give in to the overpriced! Corporate! Mainstream! I can get better for cheaper Ipad! Wait, what was i saying again? Oh yeah, Ipads are greeeeeaaaaaaaat....  Well there's not much point in complaining now anyway, I've already ordered one, and a case, oh and a stylus, ok fine i am a little excited.
   Well anyway lets get to the task at hand, What app should i use? Should i use just the one? A series of apps? Or am i better using an app to start, and then finishing it using my pc Bamboo? I've looked on a few websites and here's a list or two of apps they recommend.

Digital arts online - Top 5
1. Adobe Photoshop Touch                £6.99
2. Art Rage for Ipad                           £2.99
3. Brushes 3                                       FREE
4. Autodesk Sketchbook Pro             £2.99
5. ProCreate- Sketch, Paint, Create    £2.99

Creative bloq - Top 5 of 15
1. Layers
2. Bamboo Paper
3. Adobe Ideas
4. Draft
5. Sketchbook Pro

App advice - First 5
ProCreate- Sketch, Paint, Create       £2.99
ArtRage                                             £2.99
Paper by FiftyThree                            FREE
iDraw                                                Roughly £6
Colored Pencils                                 Roughly £2.50

Petshopboxstudio Top 6
1. ArtRage                                        £2.99
2. Brushes
3. Sketchbook
4. Layers
5. ArtStudio
6. ProCreate                                     £2.99

So from what I've gathered by looking at a few websites is, that everyone has different ideas when it comes to the best app, so i guess I'm just gonna have to give a few a go and see which one suits me the best, also if anyone has any suggestions please feel free to let me know, it would be much appreciated, cheers.