Unfortunately the stack exchange format doesn't really facilitate "discussion" but I'll try to give you an answer of objective statements that might help inform a decision!
Bretonnia: The army book is from 2003, so are most of the models. There aren't even any rumors that there will be an update soon. Heavy Cavalry overall was significantly weakened in the eighth (current) edition core rule book.
Dwarves: Army book authors try to spice it up a little bit, but fundamentally this army is about blocks of tough little dudes who trundle forward slowly while they shoot you up. Some players are really into the thematic elements and love the traditional high fantasy dwarfy legion. Others think it's just plain boring to have an army that spends a lot of its game turns saying "walk forward, shoot, your turn go." You have to decide which you are.
Dwarves also tend to be covered head to toe in metal, which makes them an easy army to paint to a nice table top standard for beginning hobbyists.
Empire: Has a lot of variety and effective armies can be built in many different ways. Swarms infantry, check, elite infantry, check, cavalry, check, shootiness, check, magic, check. The downside of that is that there are also plenty of combinations that aren't effective and you can end up owning a lot of expensive models that you don't use if you shop without a plan towards a final working army list. Look at army lists on a Warhammer discussion forum and maybe seek some advice on an army list, then build a shopping list from that. (Unless you're just rich or something, then go to town)
WHFB vs WH40K is totally a regional thing. Different cities/stores have different balances of # of people playing one game or the other and it shifts around over time.