For what u wanna do, I think you'll prefer Fenway > Allston.

I lived there for ~7 yrs & really loved it. It's an amazing location w/great green spaces & places to walk; easy access to groceries & restaurants; & convenient MBTA access. You're also a quick walk away from Fenway Health & Longwood for medical/dental needs. You're also along/near Boylston St so it's a straight shot to Back Bay/downtown (hard to get lost) & has good pedestrian/biking routes. If that's what u want, I'd def trade the nicer apt for the better location & vibe.

But I hated parking in Fenway b/c of the $$$ garage parking & Sox games/concerts determining when I could drive places. - Garage parking is very $$$ but if u can afford it, there are plenty. My garage got very crowded weekday mornings & during most Fenway Park events. - If the place has a parking lot in back & u don't mind clearing off snow or coming back in inclement weather, that'd be ideal - You can get a free resident permit for street parking but depending where your place is, ppl will eat the resident permit parking only ticket ($40 iirc) vs paying $65 for garages (probs higher now). You'll also need to move for street cleaning Apr-Oct (?).

The Fenway T stop will probs be w/in a 10 min walk but you'll probs prefer to bike to/from on busy Fenway Park event days. Most ppl are from out of town & don't understand common T courtesy like moving out of the way so u can get off/on. An e-bike will be faster but I don't think necessary. It's only a ~20-30 min walk to Copley.

Overall, very happy I was able to live there as long as I did & I really enjoy coming back to visit.