On top of what Slottery said, be careful with that strat, there are plenty of bonus T&C's that specifically forbid that (per maximum coinsize allowed) so make sure you read the fine print...
Whatever Bonus WR, i mostly just play my usual suspects, which are mostly the high/extremely volatility slots such as DOA, DOA2, Lil Devil, Jammin Jars, any and all Nolimit Games of late, etc.
Specifically keep the betsize modest, say 1 euro per spin on a 1500 balance, as with these slots, if you hit a really good one, that is more than enough to give you a fair chance of making WR.
Mind you: some of the slots i mentioned do appear on certain T&C's as excluded. or as 'not counting towards WR', so again, make sure to read the fineprint.
I usually don''t even get Bonus Money anymore, as the places i play the most give me those bonuses you unlock by wagering your own cash, and when you do, the bonus is added as cash (so you don't have it as extra balance when you start the session)
I.e deposit 100, get 50 bonus but only after you wagered your own 100,- between 15 to 30 times, and when you do, its umlocked, to claim as cash. I really prefer this format, especially since i can play whatever i want, do bonus-buys, big bets and whatever.
Surely depends on the Casino/loyalty level, but this is the case for me...
Good luck with the WR!