What is the best trade for combat engineers and can make a full career out of the royal engineers ?

No-one can really say what the best trade is as it will depend on each individual; on their likes and dislikes, hobbies, sports, opportunities taken, it might depend on the unit they're at - there are just so many variables. My advice is, do your research and match it up to what you enjoy doing (your Candidate Support Manager or local Army Careers Centre staff could help with this). Anyone can make a full career in any capbadge - again, this depends on the individual; work ethic, working well with others, self motivation, selfless commitment etc (ie the embodiment of the Army's values and standards) and really importantly, maintain a good sense of humour!