It's not necessary to have transit visa if your flight departs from the same airport irrespective of the terminal. As I have posted earlier, if you are at heathrow airport say you land at terminal 1 and your connecting flight is from terminal 4, you need not apply for transit visa as you do not need to pass immigration point. You can travel within airport (Heathrow airport provides bus service from one terminal to another free of charge).
http://www.ukba.homeoffice.gov.uk/visas-immigration/transitthroughtheuk/visa-to-transit-landside/
If your halt is of only 4 to 10 hours, it's advised not to even apply for transit visa as you would need to again check in and go through security and blah blah...
if your flight is from a different airport, then yes you will need a transit visa and you just need to show your connecting flight's ticket (usually not recommended to have such travel plan).
Now, talking about the routes, it all depends on the airline you are booking. If you are booking lufthansa, it will most likely go via germany. If you are booking Swiss airline, it will go via Switzerland, jet usually goes via london. airindia via USA and so on. it's good to have a connecting flight coz flying for flat 18 to 20 hours can be pain in the a**. Though ensure halt is not of more than 3 to 4 hours.
Now also for those people who have halt of 4.5 or more and not willing to go out of the airport, please check with respective airports as they have a private lounge for people with a halt of 4.5 or more hours such as Dubai, Swiss(irrespective of your airline or travel class) and in these private lounges you get free drinks (hard and soft drinks) and so on...
now talking about airlines... lufthasa, jet all are good... as far as student discounts are concerned, yes you can try but most of the times, they are tricky...now the trick is, they offer you discounts (but condition is the carrier should be that airline through out, say if you book Lufthansa - the low fair tickets will be connecting flights and carriers will be two, hence discount doesn't apply/ a flight operated by lufthansa through out will be an expensive one so you won't buy it anyway).
My opinion, Indian Airline is good as majority (i guess actually all) their flights going to Canada go via US and they are the only carrier (through out - no co-operation).
Cheers!
