Both my Handi 22 mag amd 17 HMR shoot very tight groups. I got the 22 mag in January and have not really put it through it's paces yet.
There is some overlap between the two cartridges IMO, especially with the mag using 30 grain bullets.
A couple of things to consider is the ballistic coefficients of the various rounds
ballistics comparisons can be found at
http://www.cci-ammunition.com/ballistics/rimfire.aspxThe mag with full weight bullets will have better knockdown then the HMR over 100 yards due to heavier bullet weight but also more drop.
Th2 lighter mag bullet will have a poorer ballistic cofficient than the full weight bullet BUT the lighter bullet will get there faster and with less drop.
The HMR has excellent ballistic coefficient and the, lighter bullet really gets there in a hurry and is extremely accurate. Best used around 100-125 yards on small varmints
It all depends on what targets you selecting and the ranges.
IMO, I would get the Mag in Handie and add a HMR barrel later if you want a really accurate flat shooter
Anyhow that's my opinion --AND you realize with this type of question you will get many valid approaches. finally. only you will have to live with the decision--Do your own research, compare the firearm, costs, ammo availability,and ultimate use.
Make your decision and don't look back. Enjoy your shooting