There's quite a few variables involved to come to the best decision but here's my take on it having built a good many of each.
For a crate motor the 207 is hard to beat for moderate power and with the right heads could be made very streetable and yet still have good power levels.
As for the 2.5 using untouched case halves I just wouldn't bother. If the cylinder walls don't crack they'll go oval and have high oil usage in no time.
I've built a good many of these so feel in a fairly good position to answer.
Had mine not had sleeves when i bought it I'd have built either a 2.1 stroker using a 2.0L block or a 2.3 stroker using an EJ22T block sourced from the UK.
If you're dead set on using a 257 then you'll need to strengthen the block somehow. I've used pins around the bores to good effect 500+at the wheels
Here's a couple of pics of my pinned block
If you're going to sleeve it then be prepared for another build maybe a couple as sleeves tend to settle and require another reface. That's not always the case but it happens enough for you to be mindful of that happening.
Another good option is having a CDB Insert done which has a similar effect to the pins i.e. it offers strength where it's needed most.
Either way the 2.5 must have good head studs they are prone to doing head gaskets if you dont.
Also bear in mind for big power the EJ257 factory sleeves are the thinnest of the lot so even if you have it pinned or closed decked you may still crack a sleeve. That's only usually applicable to big power builds though.
The 2.5 is a good option but only if its done right and doing so gets expensive. if you cut corners on a 257 build I guarantee it will come back and bite you.
I think the best bang for buck option is a 2.1 stroker. Best option would be to use a CDB but I understand getting the rear thrust conversion is an issue here.
Personally I'd have no problem with running a forged 2.1 stroker using 207 case halves and having it sit around 500hp. It will have plenty of torque and rev like a dremel. The sleeves on a 207 are the thickest of the lot too.