This all comes down to desired budget, product pedigree and support level.
On the bottom end, you can likely accomplish what you need well enough with cheap Mikrotik RB, Ubiquiti ER or an x86 whitebox running a community distro like pfSense, but there's very little support included in that sales channel unless you buy it from a VAR/MSP or vendor-direct separately (pfSense).
A step up support-wise would be Cisco RV, Draytek, Zyxel and similar (I'd avoid sub-standard products like Linksys LRT or TP-Link TL). You'll pay a bit more but get some basic chat/phone support and hardware coverage bundled in, and most products in this class are fairly well bug-fixed (multi-WAN is not child's play). Tops in the class for usability and support would probably be Peplink.
At the top end you have true enterprise firewalls and services routers (Fortinet, Palo Alto, Cisco ISR, Juniper SRX, etc.). Top-notch hardware and battle-tested software stacks with contract-based TAC support. If the business is serious enough and/or has its own IT department, this is likely the class of kit you'll be looking at.
All have their strengths. Considering the type of product you're thinking of already, I'd lean towards a Cisco RV340 series or a Peplink Balance, or just hire the whole project out to a local MSP and have them just handle it with whatever gear they routinely use.