Either board is fine. Go with whichever one better fits your budget. The Mortar Titanium is probably the better board but it is apparently no longer in production or being actively sold in most places. I personally prefer ASRock over MSI in most cases but it's almost a tossup in this case. The Mortar boards seem to have slightly better performance when it comes to VRM throttling according to reviews but for a soft overclock, which might not even be necessary based on the stock boost features for that platform, it probably doesn't even factor in between these boards.
Either is ok. Go with the board you like better visually and whichever has better regional support in your area in the event anything goes wrong. I think MSI is a lot better represented in the eastern regions.
I have a B450M Steel Legend paired with a 2400G. For the money it's okay. In fact it's a bargain. But it has a few glitches and 3 months after initial release it sill has some issues:
The RGB lighting is flaky and they haven't fixed it. A lot of the patterns on RGB Channel 2 will not light the assigned colors. Their last update (1/29/2019 V2.04) leaves the motherboard ARGB ON when the motherboard is shut down. That is just sloppy and in my book unexcusable.
The FastBoot option when turned on just dumps you into the UEFI everytime. Again another primary basic feature they failed to check.
My XPG 3000 memory will only run at 2866. But I have 4 banks populated and this speed is well beyond spec for Raven Ridge. Raising Voltage to 1.4 didn't help. Also the timings were all wrong. I had to hand enter them.
The overclocking & fan utility is painfully limited. And there is no auto overclocking option. UEFI menus can be confusing to navigate compared to other vendors. You REALLY have to look for some options. But tech support will guide you to what you are looking for.
I can get it to clock to 3.8 all cores on the 2400G which is about average.
That said, the 2400G was a placeholder for Navi And Zen 2 (Ryzen 3000)
1. I booted and installed windows flawlessly on the first system install. That includes 1 NVME 12 Fans and 1 SSD and 32GB mem
2. The motherboard is extremely firm. It felt solid and it's a big improvement over the ASRock of old.
3. The VRM is more than adequate.
4. The fan headers are designed for high current. This makes them a good choice for Water Pumps. Unfortunately their fan software doesn't allow you to designate what kind of device is connected to the fan headers. So Fan Header 1 can't be labeled CPU Fan and Fan Header 2 can't be labeled Water Pump and Fan Header 3 can't be labeled Rear Exhaust. The software doesn't allow you to see the fan speed compared to the temperature sensor.
Now I'm used to buying Premium motherboards (Like Asus TUF) that cost over $300. So to pick up this board for $80 it's not really a fair comparison. But for the money it delivered specs and is solid. Windows has yet to blue screen. Just don't expect it to do miracles.