A quick comparison of two popular 5.5m midfield options. Most are looking at ASM or Armstrong for that slot and I thought I'll just do a quick analysis.
Here's comes 'The Thread'
Here's comes 'The Thread'
First let's look at their fixture run
ASM : Whu, BHA, Tot, BUR, MUN, Wol
Armstrong: Cry, TOT, Bur, WBA, Che, EVE
Both set of fixtures look fairly similar with the Saints' run looking slightly better.
ASM : Whu, BHA, Tot, BUR, MUN, Wol
Armstrong: Cry, TOT, Bur, WBA, Che, EVE
Both set of fixtures look fairly similar with the Saints' run looking slightly better.
To analyse that fixture run a little more, we'll check the goals conceded per game on average for each of their opponents
ASM: 1.6, 1.4, 1.2, 1.1, 0.9, 1.1 = Total 7.3 goals.
Armstrong: 1.3, 1.2, 1.1, 1.0, 1.4, 1.5 = Total 8.5 goals.
Better run as expected for Armstrong & Soton
ASM: 1.6, 1.4, 1.2, 1.1, 0.9, 1.1 = Total 7.3 goals.
Armstrong: 1.3, 1.2, 1.1, 1.0, 1.4, 1.5 = Total 8.5 goals.
Better run as expected for Armstrong & Soton
Let's compare their heatmaps from last season! Operating on opposite flanks we aren't seeing a lot of differences here as well. The Saints man a little more present centrally compared to ASM
Let's look at their key stats from last season (taken from @FFH_HQ)
ASM

Mins - 1,860
Pts - 92
3
5 
Shots - 46 (SiB 14)
SoT - 21
Big chances - 5
xG - 5.17
Final 3rd passes - 216 (77% successful)
Key passes - 33
Big chances created - 8
xA - 5.3
xPts - 113.3
ASM


Mins - 1,860
Pts - 92
3


Shots - 46 (SiB 14)
SoT - 21
Big chances - 5
xG - 5.17
Final 3rd passes - 216 (77% successful)
Key passes - 33
Big chances created - 8
xA - 5.3
xPts - 113.3
Armstrong 
Mins - 1,706
Pts - 98
5
4 
Shots - 46 (SiB 14)
SoT - 20
Big chances - 3
xG 4.21
Final 3rd passes - 218 (65% successful)
Key passes - 18
Big chances created - 2
xA 2.29
xPts - 102.3
Extremely similar goal threat numbers but ASM wins out with better creativity

Mins - 1,706
Pts - 98
5


Shots - 46 (SiB 14)
SoT - 20
Big chances - 3
xG 4.21
Final 3rd passes - 218 (65% successful)
Key passes - 18
Big chances created - 2
xA 2.29
xPts - 102.3
Extremely similar goal threat numbers but ASM wins out with better creativity
Let's quickly compare the two players post restart to see better "recent" form
Player comparison tool from @FFH_HQ
Again very similar stats, ASM better at the creativity stats whereas Armstrong slight better at goal threat post restart
Player comparison tool from @FFH_HQ

Again very similar stats, ASM better at the creativity stats whereas Armstrong slight better at goal threat post restart
Lastly we'll just see a few stats for the teams they play for and their goal involvement
ASM

Team goals - 38
xG - 36.49
% GI - 21.1
Armstrong
Team goals - 51
xG - 56.5
% GI - 17.6
Saints clearly the better attacking team but ASM with more GI for their team
ASM


Team goals - 38
xG - 36.49
% GI - 21.1
Armstrong

Team goals - 51
xG - 56.5
% GI - 17.6
Saints clearly the better attacking team but ASM with more GI for their team
To conclude, not a lot to separate them. I prefer ASM slightly more due to better chances at assists. Armstrong has a slightly easier fixture run, but with Ings /Adams also hogging the pts at Soton, ASM can be the one involved more in terms of FPL returns. Hope this helps!