Michael
After a lifetime of GSDs, owning and training Malinois (in the last three years) is very much a learning curve. I enjoy working them and they are a breed which certainly enjoys and needs to be worked, however unless you can get some good advice and see what’s involved with this breed, I’d say stick with the devil you know. Now it’s quite true that getting a good working line
GSD is not that easy, but it’s not impossible and there are a few breeders on here who breed good WL GSDs.
You also have to be realistic about your situation at home; have you got kids, are you going to kennel outside, are your neighbours whingers, can you devote the time to training, etc. Just some of the questions you may want to ask yourself.
I’m not trying to be off-putting, I just think that working bred dogs of either breed are a totally different proposition if you’ve never experienced them before; especially Mals.
Before you make any decision, as Adam says, do your research and speak to as many people as possible, see as many dogs as possible, and when you decide try to take an experienced person with you before making any commitment money wise.
Finally, IMO I’d prefer a pup than a trained adult. You at least know what you’ve put into it, so called “Trained Dogs” come with their own problems which some "trainers" may be reluctant to enlighten you about.
Good luck, and take your time.