What other requirements do you have? Is your house pre-wired for a system or do you have nothing?
My main thing would be to stay away from the national chain security places (Brinks, ADT, etc.) as they saddle you with long term contracts with draconian terms. On the plus side, they'll "give" you a "free" system as part of the agreement.
I have a fairly "generic" system based on an older DSC panel that's monitored by a local alarm company (via cellular) for.. about what SimpliSafe charges for their high roller plan ($27/month). I own the hardware, so like SimpliSafe, if I want to modify or add to the system, then it's on me to do so. Since my system was installed by the prior owners of the house, I'm not sure what it would cost to do, but I can also see the SimpliSafe sensors getting expensive for the number of windows I'd need to cover.
I've also integrated the system with my home automation setup (SmartThings), so that's been a plus as well.
Not sure this is super helpful - I suppose SimpliSafe is an option, but it also might be worth getting a *local* alarm company to come out and give you a quote. You can customize their install and they should have both wired and wireless options.