If you're trying to get your crankbait down deep fluoro would trump mono because it sinks....Mono has more stretch, and as stated above, will allow you to use a less technique specific rod....Remember that line size and diamater has a lot to do with how deep your crankbait will run....If you're fishing really open water without many snags or brush for a fish to tangle you up in, you can get by with 8 or 10lb....If youre going to be bumping logs or rocks, you might go with 12 or 15lb to get the fish out of it and also for a little more abrasion resistance...Personally I use 12lb Seaguar Invizx but have also used 12lb BPS mono and had no trouble with it