I would not recommend soldering the wires from the amp to the speaker. As already stated, crimp connectors work just fine. Secondly, a good solder job is fine but an average or poor solder job will fail pretty quick. The insulated crimp on connectors are a buck or two more than the cheapo exposed connectors.
Also remember you're going to have to tune the amp. If you use a multi-meter to tune or a DD-1 distortion meter you will need somewhere to connect the meter leads. I use the male end of spade connectors on the amp end for just that reason. It's also easier if you ever swap speakers or decide to move wires around for whatever reason in the future.
Freedom isn't free, remember to thank a vet.
2018 CVO RG lava orange, 117 Stage 3, 14" F47 and a few chrome extras. Boom crap gone.
2016 RG Special Cosmic Blue, 120ST with Dragos 2:1 and TTS tuner, FBI drop seat kit and JNR air ride. Stock audio long gone.