that depends on your budjet really what the difference in the price? or where would you prefer? have you seen anywhere you'd like to book?

We have been to H10 lanzarote gardens and love it but its working out quite expensive.

The diffrence between doin allocation on arival and the H10 is about £150.

Thats on alpharooms

We used to go on allocation on arrival holidays and was always happy with the results but in later years, we have chosen our accommodation so now we are a bit fussier.
Tenerife has some lovely places to stay but obviously some not so nice - mainly due to the location!
I would therefore suggest you pay the extra to make sure you get what suits your needs - when you work out the costs on a daily basis it is just over £20 per day and once you are there, I am sure you will be glad you did!