There are several points. Assuming both are say 1977 and similarly equipped the NADA base values are Allied 35600, and Tayana 30700 without counting any extras.
I am not sure that I would attach to much weight to the accuracy of those figures, but from observation would say the Tayanas tend to ask more say 60k and sell for much less, say 40k whereas the equivalent Allied may be 50k and sell for 40K.
Maybe the Allieds price more realistically, but both end up much the same.
You are talking of a liveaboard with some cruising. Both are ocean going - the Tayana certainly is, the Allied with some reservations potentially.
To a degree it depends on the balance and where you intend to go and how much, whether you favour blue water capability or liveaboard comfort.
The Tayana seems a bit bigger inside and better fitted out. However with that bowsprit you are looking at higher berth costs.
Blue waterwise the Tayana is heavier with a higher ballast ratio, but the displ/length are quite close, and the Tayana has a higher SA/displ at 18 v 17. However the motion comfort is 38.4 for the Tayana v 30.4. I don't think the differences are major but the Tayana should be a bit faster stiffer and more comfortable.
Of more concern to me would be the cockpit volume on the Allied. A large cockpit is ok for swanning around but not filling with water.
I think with those concerns in mind on some of the later Allied Princess boats, the keel was deepened by 7 inches and a 1000 lb added to the ballast. As I recall the transom was strengthened and bigger cockpit drains installed, all changes better fitting her to ocean going. However even with those she still lags the Tayana. In fact it makes her displ/L higher than the Tayana and SA/displ less. I think only a limited number of boats were modified and I have never seen one advertised with those specs so I suspect most brokers don't know they exist and just use standard figures.
Either boat is ok for limited cruising but I would think the Tayana is better fitted out and a better more stable ocean boat, albeit with that bowsprit and bigger sails.
There shouldn't be a 20k difference is selling price if they are equal in gear and condition. They should be similar with maybe the Tayana a bit higher as they are often reasonably equipped.
If the Allied suits what you will be doing and you would be paying 20k less that goes a fair way towards upgrading.