deni There's lots of different bonding agent on the market and each person will support one or the other.
Personally I to use various bonding agent for various jobs but mainly these three.
The Bonding paste is really good stuff and make a strong ridged joint but needs to be mixed with eather catalyst or hardener so can be messy.
The "Stixall" is a very good silicon adhesive and remains flexible so is ideal for fixing down fuel tanks and windscreen but at around £6 per tube it's not cheap.
At just over £2 per tube "Pinkgrip" it a inexpensive filler/adhesive that is easy to use, takes a while to set, holds well but it's not flexible, also it's self life once opened is short.