I can code in three languages/platforms: Java (its been long time), ruby on rails (beginner) and Drupal/PHP (beginner). This app is a pet project I really want to complete and involves some good business logic as well as need to have nice front end.
I really cannot decide which platform to chose. I have done some work in RoR and some in Drupal and I have not been able to make up my mind about what is the way to go.
There is absolutely no connection between languages and the fact that you want to do a webapp all by yourself and that it will involve some business logic and a nice UI. Choose the language you feel most comfortable with.
Use the platform which you enjoy working with the most. I've worked on these types of projects and you first and foremost need to have fun with it - if you don't you'll likely never finish it. All the options you have here will work fine for a web app, so just go for it :)
Evaluate your options and choose the platform that best suites you. There is a good reason there are so many web development frameworks out there. There is no be-all-end-all. They will all do what you want, it's just a matter of how you use them.
You have 2 simple options:
It really is that simple and we cannot tell you to pick one or the other. There are too many factors and it all boils down to what you want. Are you trying to learn a language if so don't go with the language you are comfortable with. Are you trying to hurry up and get this "pet" project complete, if so pick the language you already know.
I'd go between ROR and Drupal/PHP. The biggest factor is your comfort with the platforms. But you should also think about what you're looking for out of the box. Do you want all the features and out-of-the-box functionality of Drupal or do you want to build everything from scratch?
If you want to build from scratch, go with Rails.
Ask yourself some questions before you want to choose a technology (Since it is your pet project you have the freedom to choose the technology you want).However there are many other reason you might want to use some other technology. First of all are you going to sell this solution or is it like you want to do this to learn something new.If learning is the purpose then choose the technology that you want to learn now.If selling is the purpose then make a business decision.
Few years back i had written a java web aap, and i felt the java web hosting was more costlier then a plain php/mysql solution.Now though the times have changed.Also i felt php/mysql could have been much faster for coding and deployment, for the small web app that i was working on then.
If you lean back towards Java, try Seam. The language choice is more personal preference than anything else, but the frameworks vary from great to painful.
If you are a java developer, you should consider grails. It is a modern java based framework.
The language you choose wont make any difference. Not much anyways, you can do whatever in each.
As for technology I would advise against Drupal. It's a heavy piece of machinery and can do a lot of things. But it's more suited as a cms that a framework for webapps. You probably want something more light, that give you free hands.
If this is your first app, I would start it with a language you feel most comfortable with. Believe me, there will be plenty that you'll learn about the web development process in general.
Once you've done this, you'll be able to evaluate whether you want to use frameworks or CMSes based on your experience in dealing with all the parts of web development.
Ruby on Rails has a CMS called BrowserCMS.
You can watch a developer talk about that at http://aac2009.confreaks.com/07-feb-2009-10-00-browsercms-patrick-peak-and-paul-barry.html.
The presenter talks about Drupal in his talk.
If you new are both PHP and Ruby but have Java background, I would suggest Ruby on Rails. But as others say, trying to compare a CMS (Drupal) and a framework (Rails) isn't logical.